Thanks for all of your input. It turned out that it is just one of those strange behavior of VFP.

The same base class grid and the framework grid classes worked just fine when I added them to the VFP base form. However, if I do the same for one of the framework forms (I tried on two of those), it returned the error. If I place the grids in a class and create an object of that class at run time, it works just fine.

The solution is that VFP somehow seeing the alias I put in the grid ControlSource as illegal value in the framework forms. It does not, however, have the problem when I add the grid to the VFP base form / class.

I would say this is a strange bug in VFP.

Thanks again.

Maia.