VB6 – Run time error ’91’

i wanted to start some MTS instances in a VB6 EXE application. i’ve added the MTS Type Library reference, and

Dim objCtx As ObjectContext
Set objCtx = GetObjectContext()

but i still get this run time error when it reaches the SetComplete line, why?
i’ve experience in using MTS in AxtiveX DLL, but i can’t use the some approach in EXE.