OPC and DCOM Configuration. Typical problems and solutions.. Tutorial.
OPC and DCOM Configuration on Windows 2008 and Windows 7
5. Typical problems
5.1 RPC server unavailable
This error means that it is impossible to establish a network connection to the RPC service.
5.2 Access denied
This error means that the current permissions are not enough to establish a connection. You should configure DCOM as described in section 4.
5.3 IOPCServerList interface not found
You should restart the computer after you install the OPC Core Components.