Thank you!, Thank you!, Thank you! and Thank you!
That solved my problem. Thank you.

>When moving a classlib between the versions, do an explicit "COMPILE CLASSLIB classlibname" before opening or using.
>
>>I am writing a class in VFP 6. I week ago I copied the class to a VFP 5 project and I used - no problem. Today, I copied the last version of the class to the VFP 5 project and I got an error when I tried to open it: "mycontainer.vcx is not an object file".
>>
>>There are 2 classes in the container. With VFP 6 I can open both classes. With VFP 5 I can open one of the classes but not the other (the one that I need, of course).
>>
>>Any ideas?