Index: DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/Version/VersionComparer.cs
===================================================================
diff -u
--- DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/Version/VersionComparer.cs	(revision 0)
+++ DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/Version/VersionComparer.cs	(revision 6903)
@@ -0,0 +1,39 @@
+// Copyright (C) Stichting Deltares 2025. All rights reserved.
+// 
+// This file is part of the application DAM - UI.
+// 
+// DAM - UI is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+// 
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+namespace Deltares.Dam.Data.Version;
+
+public abstract class VersionComparer
+{
+    /// <summary>
+    /// Test is a current version number is greater or equal to a required version number 
+    /// </summary>
+    /// <param name="currentVersion">The current version</param>
+    /// <param name="requiredVersion">The required version</param>
+    /// <returns>True if greater or equal, else false</returns>
+    public static bool IsVersionGreaterOrEqual(string currentVersion, string requiredVersion)
+    {
+        var current = new System.Version(currentVersion);
+        var required = new System.Version(requiredVersion);
+
+        return current >= required;
+    }
+}
\ No newline at end of file
Index: DamClients/DamUI/trunk/src/Dam/Application/Program.cs
===================================================================
diff -u -r6436 -r6903
--- DamClients/DamUI/trunk/src/Dam/Application/Program.cs	(.../Program.cs)	(revision 6436)
+++ DamClients/DamUI/trunk/src/Dam/Application/Program.cs	(.../Program.cs)	(revision 6903)
@@ -20,9 +20,13 @@
 // All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using System.Drawing;
 using System.Text;
+using System.Windows.Forms;
 using Deltares.Dam.Data.License;
+using Deltares.Dam.Data.Registry;
+using Deltares.Dam.Data.Version;
 using Deltares.Dam.Forms;
 using Deltares.Geometry.Forms;
 using Deltares.Geotechnics.Forms;
@@ -61,6 +65,8 @@
 
         private static void Start()
         {
+            VerifyInstallation();
+
             DamLicense.CheckoutLicense(dAuthFeature, info.AssemblyVersion);
 
             // Parameters are used for splash screen
@@ -84,6 +90,55 @@
             DamLicense.CheckinLicense();
         }
 
+        /// <summary>
+        /// Check if the application is properly installed by verifying the required versions
+        /// of Common Files and DS_Flex in the registry.
+        /// If not, show an error message and exit the application.
+        /// </summary>
+        private static void VerifyInstallation()
+        {
+            const string requiredVersionCommonFiles = "26.1";
+            const string registryPathCommonFiles = "SOFTWARE\\WOW6432Node\\Deltares\\";
+            const string registryKeyCommonFiles = "Common Version";
+            const string requiredVersionDsFlex = "7.9";
+            const string registryPathDsFlex = "SOFTWARE\\WOW6432Node\\WL | Delft Hydraulics\\DS_Flex\\";
+            const string registryKeyDsFlex = "InstallerVersion";
+            
+            var errorMessages = new List<string>();
+            // Check version of Common Files
+            string versionCommonFiles = RegistryReader.GetRegistryValueFromLocalMachine(registryPathCommonFiles, registryKeyCommonFiles);
+            if (string.IsNullOrEmpty(versionCommonFiles))
+            {
+                errorMessages.Add("Common Files not found.");
+            } else if (!VersionComparer.IsVersionGreaterOrEqual(versionCommonFiles, requiredVersionCommonFiles))
+            {
+                errorMessages.Add("Common files version is outdated: " + versionCommonFiles + 
+                                  ". Required version is " + requiredVersionCommonFiles + " or higher.");
+            }
+            // Check version of DS_Flex
+            string versionDsFlex = RegistryReader.GetRegistryValueFromLocalMachine(registryPathDsFlex, registryKeyDsFlex);
+            if (string.IsNullOrEmpty(versionCommonFiles))
+            {
+                errorMessages.Add("DS_Flex not found.");
+            } else if (!VersionComparer.IsVersionGreaterOrEqual(versionDsFlex, requiredVersionDsFlex))
+            {
+                errorMessages.Add("DS_Flex version is outdated: " + versionDsFlex + 
+                                  ". Required version is " + requiredVersionDsFlex + " or higher.");
+            }
+            if (errorMessages.Count > 0)
+            {
+                var errorMessage = new StringBuilder();
+                errorMessage.AppendLine("The application cannot be started because it is not properly installed. Please reinstall the application.");
+                foreach (string msg in errorMessages)
+                {
+                    errorMessage.AppendLine(msg);
+                }
+
+                MessageBox.Show(errorMessage.ToString(), "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
+                Environment.Exit(0);
+            }
+        }
+
         private static void MainFormTextChanged(object sender, EventArgs eventArgs)
         {
             var mainForm = sender as MainForm;
Index: DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data.Tests/Version/VersionComparerTests.cs
===================================================================
diff -u
--- DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data.Tests/Version/VersionComparerTests.cs	(revision 0)
+++ DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data.Tests/Version/VersionComparerTests.cs	(revision 6903)
@@ -0,0 +1,62 @@
+// Copyright (C) Stichting Deltares 2025. All rights reserved.
+// 
+// This file is part of the application DAM - UI.
+// 
+// DAM - UI is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+// 
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using Deltares.Dam.Data.Version;
+using NUnit.Framework;
+
+namespace Deltares.Dam.Data.Tests.Version
+{
+    [TestFixture]
+    public class VersionComparerTests
+    {
+        [Test]
+        public void IsVersionGreaterOrEqual_ReturnsTrue_WhenCurrentIsGreater()
+        {
+            Assert.That(VersionComparer.IsVersionGreaterOrEqual("7.8.1.2", "7.8.0.0"), Is.True);
+        }
+
+        [Test]
+        public void IsVersionGreaterOrEqual_ReturnsTrue_WhenCurrentIsEqual()
+        {
+            Assert.That(VersionComparer.IsVersionGreaterOrEqual("7.8.0.0", "7.8.0.0"), Is.True);
+        }
+
+        [Test]
+        public void IsVersionGreaterOrEqual_ReturnsFalse_WhenCurrentIsLess()
+        {
+            Assert.That(VersionComparer.IsVersionGreaterOrEqual("7.7.9.9", "7.8.0.0"), Is.False);
+        }
+
+        [Test]
+        public void IsVersionGreaterOrEqual_ReturnsTrue_WhenCurrentHasFewerSegmentsButIsEqual()
+        {
+            Assert.That(VersionComparer.IsVersionGreaterOrEqual("7.8.1", "7.8.1.0"), Is.False);
+        }
+
+        [Test]
+        public void IsVersionGreaterOrEqual_ThrowsFormatException_WhenVersionIsInvalid()
+        {
+            Assert.Throws<ArgumentException>(() => VersionComparer.IsVersionGreaterOrEqual("invalid", "7.8.0.0"));
+            Assert.Throws<ArgumentException>(() => VersionComparer.IsVersionGreaterOrEqual("7.8.0.0", "invalid"));
+        }
+    }
+}
\ No newline at end of file
Index: DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data.Tests/Registry/RegistryReaderTests.cs
===================================================================
diff -u
--- DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data.Tests/Registry/RegistryReaderTests.cs	(revision 0)
+++ DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data.Tests/Registry/RegistryReaderTests.cs	(revision 6903)
@@ -0,0 +1,81 @@
+// Copyright (C) Stichting Deltares 2025. All rights reserved.
+// 
+// This file is part of the application DAM - UI.
+// 
+// DAM - UI is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+// 
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using Deltares.Dam.Data.Registry;
+using Microsoft.Win32;
+using NUnit.Framework;
+
+namespace Deltares.Dam.Data.Tests.Registry
+{
+    [TestFixture]
+    public class RegistryReaderTests
+    {
+        private const string testKeyPath = @"SOFTWARE\\DeltaresDamTest";
+        private const string testValueName = "TestValue";
+        private const string testValueContent = "TestContent";
+
+        [SetUp]
+        public void SetUp()
+        {
+            using RegistryKey key = Microsoft.Win32.Registry.CurrentUser.CreateSubKey(testKeyPath);
+            key!.SetValue(testValueName, testValueContent);
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            Microsoft.Win32.Registry.CurrentUser.DeleteSubKey(testKeyPath, false);
+        }
+
+        [Test]
+        public void GetRegistryValue_ReturnsValue_WhenKeyAndValueExist()
+        {
+            string result = RegistryReader.GetRegistryValueFromCurrentUser(testKeyPath, testValueName);
+            Assert.That(result, Is.EqualTo(testValueContent));
+        }
+
+        [Test]
+        public void GetRegistryValue_ReturnsEmpty_WhenKeyDoesNotExist()
+        {
+            string result = RegistryReader.GetRegistryValueFromCurrentUser("SOFTWARE\\NonExistentKey", testValueName);
+            Assert.That(result, Is.EqualTo(string.Empty));
+        }
+
+        [Test]
+        public void GetRegistryValue_ReturnsEmpty_WhenValueDoesNotExist()
+        {
+            string result = RegistryReader.GetRegistryValueFromCurrentUser(testKeyPath, "NonExistentValue");
+            Assert.That(result, Is.EqualTo(string.Empty));
+        }
+
+        [Test]
+        public void GetRegistryValue_ReturnsStringRepresentation_WhenValueIsNotString()
+        {
+            using (RegistryKey key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey(testKeyPath, true))
+            {
+                key!.SetValue("VersionValue", "7.8.0.0", RegistryValueKind.String);
+            }
+
+            string result = RegistryReader.GetRegistryValueFromCurrentUser(testKeyPath, "VersionValue");
+            Assert.That(result, Is.EqualTo("7.8.0.0"));
+        }
+    }
+}
\ No newline at end of file
Index: DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/Registry/RegistryReader.cs
===================================================================
diff -u
--- DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/Registry/RegistryReader.cs	(revision 0)
+++ DamClients/DamUI/trunk/src/DamClientsLibrary/Deltares.Dam.Data/Registry/RegistryReader.cs	(revision 6903)
@@ -0,0 +1,66 @@
+// Copyright (C) Stichting Deltares 2025. All rights reserved.
+// 
+// This file is part of the application DAM - UI.
+// 
+// DAM - UI is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+// 
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using Microsoft.Win32;
+
+namespace Deltares.Dam.Data.Registry;
+
+public abstract class RegistryReader
+{
+    /// <summary>
+    /// Reads a string value from the Windows registry for the local machine.
+    /// </summary>
+    /// <param name="registryPath">The path to the key</param>
+    /// <param name="valueName">The name of the key</param>
+    /// <returns>The value or empty string if key is not found </returns>
+    public static string GetRegistryValueFromLocalMachine(string registryPath, string valueName)
+    {
+        using RegistryKey key = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(registryPath);
+        return GetRegistryValue(key, valueName);
+    }
+
+    /// <summary>
+    /// Reads a string value from the Windows registry for the current user.
+    /// </summary>
+    /// <param name="registryPath">The path to the key</param>
+    /// <param name="valueName">The name of the key</param>
+    /// <returns>The value or empty string if key is not found </returns>
+    public static string GetRegistryValueFromCurrentUser(string registryPath, string valueName)
+    {
+        using RegistryKey key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey(registryPath);
+        return GetRegistryValue(key, valueName);
+    }
+
+    private static string GetRegistryValue(RegistryKey key, string valueName)
+    {
+        var stringValue = "";
+        if (key != null)
+        {
+            object value = key.GetValue(valueName);
+            if (value != null)
+            {
+                stringValue = value.ToString();
+            }
+        }
+
+        return stringValue;
+    }
+}
\ No newline at end of file