Reliance SCADA connects to an OPC server but does not receive valid data

January 3, 2012

This problem is most often caused by the DCOM settings. You can solve it by adding Everyone and ANONYMOUS LOGON to the list of users in DCOM security.

1. Both the OPC client and the OPC server run on the same computer
2. The OPC client runs on a computer other than the one on which the OPC server runs

1. Both the OPC client and the OPC server run on the same computer

1. Run dcomcnfg.exe from the command prompt.
2. In the Component Services window, click My Computer and choose the Properties command from the popup menu.


Component Services

3. On the COM Security tab, click the Edit Default button in the Access Permissions group.


COM Security

4. In the Access Permission dialog, add a user named Everyone and allow local access.


Access Permission

5. On the COM Security tab, click the Edit Limits button in the Access Permissions group.


COM Security

6. In the Access Permission dialog, add users named Everyone and ANONYMOUS LOGON and allow local access.


Access Permission



Access Permission

7. On the Default Properties tab:
   Set the Default Authentication Level to Connect (or None if OPC communication is not working with Connect).
   Set the Default Impersonation Level to Identify.


Default Properties

2. The OPC client runs on a computer other than the one on which the OPC server runs

A) On the computer where the OPC server runs

1. Run dcomcnfg.exe from the command prompt.
2. In the Component Services window, click My Computer and choose the Properties command from the popup menu.


Component Services

3. On the COM Security tab, click the Edit Default button in the Access Permissions group.


COM Security

4. In the Access Permission dialog, add a user named Everyone and allow both local and remote access.


Access Permission

B) On the computer where the OPC client runs

1. Run dcomcnfg.exe from the command prompt.
2. In the Component Services window, click My Computer and choose the Properties command from the popup menu.


Component Services

3. On the COM Security tab, click the Edit Default button in the Access Permissions group.


COM Security

4. In the Access Permission dialog, add a user named Everyone and allow both local and remote access.


Access Permission

5. On the COM Security tab, click the Edit Limits button in the Access Permissions group.


COM Security

6. In the Access Permission dialog, add users named Everyone and ANONYMOUS LOGON and allow both local and remote access.


Access Permission



Access Permission

7. On the Default Properties tab:
   Set the Default Authentication Level to Connect (or None if OPC communication is not working with Connect).
   Set the Default Impersonation Level to Identify.


Default Properties

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