Hello,
this is difficult to diagnose without having in reproduced locally. The OPC Automation DLL may use different parameters when instantiating the server. The problem comes to us from the OPC Server, we do not directly generate it.
I can see following "wild" guesses:

It can be inderectly caused by a security problem. Can you please check, comparing the working and non-working scenario, the user account under which the OPC server process, and possibly other relevant pieces are running? (from Task Manager). If they differ in user accounts, or if some processes don't appear at all, between the two scenarios, then this may be the clue to the problem.
There is a thread on OPC Foundation board www.opcfoundation.org/forum/vi... with similar issue. You can try (in the EasyOPC Options Utility) setting the allowed execution contexts for OPCEnum and for OPC Servers just to "Local server", and uncheck all the other options. The settings are on the "OPC-DA Globals" tab, under "Machine Parameters" and "Client Parameters" groups.

Just as a note, a guy with similar problem with Archestra (but a different server): www.plctalk.net/qanda/showthre... - but no solution there.
Best regards,

Hello, can you please describe the details of your problem, or add the missing attachment?