DCOM errors typically begin with a "0x800" code. Specifically, the 0x80040202 error appears in the OPC Client application when it fails to receive a callback from the OPC Server. The OPC Training Institute’s website has a whitepaper that provides details on this error its various potential causes, and how to solve them using a step-by-step guide.
For automated troubleshooting, refer to OPC Expert, a software application to troubleshoot OPC connections. If OPC Expert fails to connect, it automatically informs you of the problem, diagnoses the cause, and suggests a solution. OPC Expert is free to download, does not require installation, and does not make any changes to Windows registry, so it is safe to use on your computer. Download at www.OpcExpert.com.