error 80040154 from coCreateinstance

[joemu...@msn.com]

I have an old activex control that is used in old-style VB and C++
applications.
This has worked flawlessly through various incarnations for the last 8
years.
I now find that the control fails to instantatiate through the call to
CoCreateInstance with an error code of 80040154 - which would normally
indicated that the control is not registered.
But, the control is most definitely registered via regsvr32. I can
search the registry based on the GUID and it has entries in all the
right places. The InProcServer points to the correct path, and I can
even see the ocx file's InitInstance break when the file gets loaded.
Interestingly, if I install the control through our InstallShield
procedure, it will come up. But if I then rebuild from the sources
and register the newly-built control, regsvr32 will report success,
but a subsequent call to CoCreateInstance will fail.
As I've stated, this failure is new because up until recently, this
was my primary development machine. I'm starting to question if this
is the result of a windows update gone bad, but all attempts to roll
back my os to a previous checkpoint have failed.
The Facts:
XP 32 bits with all the latest updates.
Build environment is VisualStudio 2005 with all the latest updates.
ActiveX test container app will list the control in its listbox, but
fail to instantiate it.
All DLL dependencies are accounted for.
The ocx file in question actually has 3 controls in it and they all
fail in the same manner.
My build procedure calls regsvr32, regtlib and aximp.
I have tried regasm but it made no difference.
I have a WinXP64 machine which does not exhibit the failure.

I've now wasted 2 days on this and need help. Any ideas would be
appreciated. Responses to this group or my email address will do
fine.

Thank you.