>>
>>Check if the class library is included on the Form Controls toolbar.
>
>not sure I understand this one. I get the problem even with nothing else open when I've just entered vfp and typed "modi class (myclass)"

Probably this is not the case then. You can add your VCXs to the Forms Toolbar by:
1. Modify any form.
2. Click on the Form Controls toolbar or go to View->Form Control Toolbar.
3. Click on the View Classes button then click Add... select any visual class library.
4. If you have a resource file, your visual class library is always included in that toolbar.

This causes the same problem for me, but not always.