I don't understand this issue enough to tell if this is relevant to zhou jie's problem, but on Python ticket 7546, Stefan Krah says: """ The poster should get the same error messages from: ml64 /c /Cx x64dll.asm Perhaps the assembly isn't MASM? """ http://bugs.python.org/issue7546# msvc9compiler.py: add .asm extension Regards, Zooko