OPC and DCOM Configuration. Typical problems and solutions.

This part is for Windows 7 and Windows Server 2008. On Windows 10, 11, Windows Server 2019 and 2022 use the current guide: 5. Troubleshooting and its DCOM settings (dcomcnfg) page. Parts of this series: 1. OPC Core Components · 2. Users and permissions · 3. Firewall · 4. DCOM settings (dcomcnfg) · 5. Typical problems.

5. Typical problems

The Windows 10 and 11 version of this list is more complete and covers the DCOM hardening update of 2022 and 2023, which also affects Windows 7 clients that talk to updated servers.

5.1 RPC server unavailable

This error means that it is impossible to establish a network connection to the RPC service.

1. If the error occurs during an attempt to get the list of OPC servers on the remote computer, you should check the firewall settings. The OpcEnum.exe file located in the Windows\System32 folder by default must be added to exceptions.
2. You should make sure that inbound DCOM connections to port 135 are permitted
3. If the error occurs during an attempt to connect to the OPC server, you should make sure that the executable file of the OPC server is added to the Windows firewall exception list.

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.

Related articles: OPC and DCOM Configuration. Typical problems and solutions.

OPC and DCOM Configuration on Windows 2008 and Windows 7

• Part 1. Installing OPC Core Components.
• Part 2. OPC and DCOM Configuration. Creating a user and giving access permissions.
• Part 3. Configuring the Windows 2008 and Windows 7 firewall for DCOM and OPC.
• Part 4. DCOM Configuration. Dcomcnfg.
• Part 5. OPC and DCOM Configuration. Typical problems and solutions.