>>I have no more ideas :o((( What happens if You recompile the Form? Or remove FoxUser.*?
>
>Compile didn't help. I guess, I just have to take this out of my mind. But I'm afraid, I would not be able to.

This is clearly something going on with the form, not with the grid. Is the form's KeyPreview set to .T.? Try setting it to .F. Also, check the form's DblClick method.