I've detected an issue using third party active controls and even ones that I make through Visual C++. Specifically the problem occurs in resize.cpp file -> CResize::SetResize() procedure. Apparently the handle being returned from the control is 0x00000000 and the code can not ::Attach() the handle to the pwnd variable.
You can easily duplicate this by inserting an ActiveX (COM) control made by you with VC++ and using it in your project OR using a third party control - Truegrid DB Ole 7.0 Add it to one of the CFormView objects you create. Add it to the static SIZING array on the InitialUpdate() of the formview, compile, run and viola' you get the Assertion error.
Any help on this issue would be appreciated, I'm guessing that this has something to do with when the Control is actually created - but then again I could be way off. I'll try adding the SetResize() to the OnInitDialog() or other areas of the CFormView and get back to you. Of course if you get a solution before I do, please post here.