I have 2 of your StandardForms. I set one to be an MDI parent and the other to be an MDI child. When I tried to set the parent property of the child it throws an exception:

Top-level control cannot be added to a control.



???

From the google searching I've been able to do on that error message, it appears you cannot add a form to another form's controls collection.  Whenever I try to reproduce this, I can only get the error message when trying to set the Parent property of the child form to the instance of the main form, which tries to add the child as a control onto the main form.  However, in an MDI environment you should use the MdiParent property, not the Parent property, which should produce the functionality you're looking for

You know, I think I knew that at some point. Thanks for reminding me.

No problem