Index: Core/Common/src/Core.Common.Controls/DataGrid/DataGridViewControl.cs
===================================================================
diff -u -r277b68e1c58f97f527567f5500be6bc39efacd97 -rbd8a4787e4ef26cf7e50d768f053fdc57f075713
--- Core/Common/src/Core.Common.Controls/DataGrid/DataGridViewControl.cs	(.../DataGridViewControl.cs)	(revision 277b68e1c58f97f527567f5500be6bc39efacd97)
+++ Core/Common/src/Core.Common.Controls/DataGrid/DataGridViewControl.cs	(.../DataGridViewControl.cs)	(revision bd8a4787e4ef26cf7e50d768f053fdc57f075713)
@@ -409,6 +409,8 @@
 
         private void DataGridViewOnCellClick(object sender, DataGridViewCellEventArgs e)
         {
+            if (e.RowIndex == -1 || e.ColumnIndex == -1) return;
+
             dataGridView.BeginEdit(true);
             ComboBox combobox = dataGridView.EditingControl as ComboBox;
             if (combobox != null)