Add an occurrence of a part to an assembly does not seem to work...

When you add an .ipt part to an .iam assembly you need to pass the correct sort of parameter to the Add function. For example this will not work:

CComPtr<ComponentOccurrence> pCyl2Occ = nullptr;

hRes = pOccurrencesList->Add (L"C:\\TEST\\Cyl2.ipt",pPosMatrix,&pCyl2Occ) ;

...but this will...

CComPtr<ComponentOccurrence> pCyl2Occ = nullptr;

hRes = pOccurrencesList->Add (CComBSTR(L"C:\\TEST\\Cyl2.ipt"),pPosMatrix,&pCyl2Occ) ;

The difference is that the first call does not cast to CComBSTR, the second, working version, does.