I got a similar error when I subclassed my pageframe. This is what the help system has to say about these errors.

Object class is invalid for this container (Error 1744)::
You have attempted to add a member object to a parent object with the AddObject method. It cannot be added because the member object’s class cannot be a member of the parent’s object class. For example, you cannot add a Grid object to a PageFrame object.

I put fox grid objects on fox pageframe objects all the time. The problem I got was when I subclassed the pageframe object. The interesting thing is that this error only shows up after edit the form in question. If you take a working form and change the classes of the controls and just run it, it will work. If you edit the form and change anything, anywhere, then you get the error. What I've done is reclass my pageframe back to a fox pageframe, make my form edits and reclass the pageframe to my baseclass again.

This is a real pain and any easier solution would help greatly.

Thanks,
Rock.