Hi Markus
You can catch the pressing of Delete key in the TableControlCurrentCellKeyDown event and make its "Handled" property true if it is a combobox column.
private void gridGroupingControl1_TableControlCurrentCellKeyDown(object sender, Syncfusion.Windows.Forms.Grid.Grouping.GridTableControlKeyEventArgs e)
{
if(this.gridGroupingControl1.TableControl.CurrentCell.ColIndex == 3)
{
if (e.Inner.KeyCode == Keys.Delete || e.Inner.KeyCode == Keys.Back )
e.Inner.Handled = true;
}
}
Attached is a sample.
DeleteComboBox_3088.zip