validation on lostfocus ..you cannot assign a null to a variable that is not ..

[tndinnc]

I have a form in datasheet view, it's source is a linked SQL table. I want to set validation so that when a users is on field that requires a number if they delete the 0 in it and tab out it forces them to enter a number. But all I ever get when anyone clears any field actually is "you cannot assign a null to a variable that is not a variant data type". All of my fiends are directly linked to a field in my linked table. So i'm not sure how to trap for that error. Any suggestions?

[June7]

Don't understand that, never encountered that message. Field should allow Null. How are you doing the validation? Is there VBA code? Post code.