Hello Francois,
Thank you for writing.
I would suggest using the
CellValidating event of the
EditorControl for your scenario:
Please give it a try and let me know if ti works for you.
Best wishes,
Stefan
the Telerik team
Q2’11 SP1 of RadControls for WinForms is available for download (see what's new); also available is the Q3'11 Roadmap for Telerik Windows Forms controls.