Hello Tooraj,
First, It is not colum1.CurrentRow, it should be radGridView1.CurrentRow,
Second, please take a look at the following very basic example of
CellValidating
You should either use the cell.ErrorText or cancel the operation, i just added them both here for clarity purposes.
Another way of doing things, as instructed by the
documentation is to handle the ValueChanging event and handling validation there.
Hope this helps, if you have any other questions or comments, please let me know,
Best Regards,
Emanuel Varga