When an OPC Client application connects to a remote computer and attempts to browse for OPC Servers, it is actually connecting to a copy of OpcEnum on the remote PC. OpcEnum retrieves the list of OPC Servers on the computer on which it resides. The inability to connect to OpcEnum is typically a result of authentication failure. There are other causes for a failure to connect to OpcEnum. These reasons are listed on the OPC Training Institute’s website in the whitepaper titled "Troubleshooting OPC and DCOM: Quick Start Guide."
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