Errors

Generally this error will occur when you are trying to create an asynchronous group. If you create a synchronous group it will work correctly.

This is due to the necessity of callbacks in asynchronous communication. Your DCOM is configured to allow communication from the OPC Client to the OPC Server, but not the other way. You must allow communication in both directions by reviewing your DCOM settings for the system defaults, OPC Client (if applicable), and OPC Server. To change these, you will have to access the DCOMCNFG tool and allow this communication. This holds true for both a user account, and the system account.  You can configure your COM and DCOM through use of the following documents (in pdf format):

DCOM on Windows NT/2000
DCOM on Windows XP/XP SP1/2003
DCOM on Windows XP SP2/2003 SP1

If you are experiencing DCOM issues across domains or while using workgroups, we strongly recommend downloading and installing MatrikonOPC Tunneller. MatrikonOPC Tunneller eliminates DCOM setup headaches and gets data flowing seamlessly between your servers and clients using TCP/IP.  Tunneller can also be used to ensure secure communication across firewalls.