Fabio, I'm not sure where you are going with your testing on this subject. I've run your two code snippets and they both run fine on my machine. Maybe I'm missing something here:

But i get a C5 if i run it without open it or do other actions (only DO bug335.prg ),
in VFP7SP1 with default options, 
in VFP6SP5 with default options.

try with this:
Define a prg for the code. 
save. 
close VFP.
open VFP.
on Command exec

What is Bug335.prg

Are you interested in what MS wrote me about the _Assign method bug? If so I'll post it in the morning.

Thanks Fabio, this has been fun.