Maybe the problem is in instancing order of objects in form class.
You should try to re-order the objects in which are added in run-time to form class.
I had a similar problem with DataEnvironment class in Form Class, and the problem was that DE class has been added last to the form container but other objects in forms (comboboxes, textboxes...) are using tables from that class and the VFP show me "Error instantiating the object." because in the moment of adding those objects the DE class don't exist. I solve this problem by moving DE class to be added first in sequence of instancing.

>I have a form baseclass that I have already subclassed once. Now I want to subclass the subclass and I've done this before but with this class I get "Error instantiating the object." with the create class command. I've done this with other forms but there are two forms that I have that I can't subclass the subclass. Does anyone know why? I looked at both forms and I don't see any reason why it would be doing this. This is in VFP 6 SP5