Is a COMException of 0x80040154 always 'Class not registered'?

Question

Does a System.Runtime.InteropServices.COMException of 0x80040154 always mean that the class isn't registered? I'm getting a COMException which says "Retrieving the COM class factory for component with CLSID {29131539-2EED-1069-BF5D-00DD011186B7} failed due to the following error: 80040154." It's trying to load Interop.Domino.dll which is a reference I got from the COM tab of Add Reference called "Lotus Domino Objects" which points to domobj.tlb in the Notes program folder.

I wrote the code years ago - it's the only thing I've ever done with interop and it's fair to say that I never really got to grips with it.

I'm seeing this error again after moving the code to a 2008 R2 server (so it's x64). It was written on XP and run on 2003 (both x86). In order to diagnose the problem, I built a Win7 x86 (because there's no R2 x86) box and it worked. I also built a 2003 x64 box and it fails with the same error, so it looks like it's caused by moving to x64 architecture. Is there something I should do when doing interop to get x86 COM DLLs to work on x64 machines?

Answer 1

Pay attention to register of 32-bit components using the correct register (C:\Windows\SysWOW64\regsvr32.exe).
If you have already registered up with the 64-bit version, unregister each dll with the same version.

More help you find here Team is Going from XP32 to XP64 for .NET Development - Any Gotchas?

Good luck