0x800706BA DCOM Error

Symptom

0x800706BA is a DCOM error that displays on the OPC client application when the OPC client determines that its connection to the OPC server is alive, but it is not.

When this error occurs, users will notice one or more of the following symptoms:

  • The OPC client application fails to create an OPC group.
  • The OPC client application is not able to show data updates. Consequently, data values remain unchanged.
  • The OPC server shows as running on the OPC server computer, but the OPC client application is not able to connect to the OPC server.

 

Cause

This error can occur in different conditions including:

  • The OPC client application launched the OPC server successfully, but due to a lack of permissions (DCOM or otherwise), the OPC client cannot access the OPC server for data. In this case, the OPC server may actually be running, but is not accessible to the OPC client.
  • The OPC server was initially running, but access was stopped. For example, the server was shut down.
  • The OPC client computer is trying to create a group, but the firewall is on for the OPC client computer.

In 0x800706BA DCOM error, the OPC server suddenly becomes unavailable to the OPC client (or simply disconnected from the OPC client application). This can happen due to any of the following factors:

  • OPC server has shut down without informing the OPC client application. This shutdown might be due to a user ending the OPC server Windows process (using Task Manager), or a crash on the OPC server.
  • OPC server becomes physically disconnected from the OPC client application. For example, someone disconnects a network cable, or a network device (such as, a hub, switch, router, and so on) fails.
  • The OPC client application is suddenly not able to receive callbacks from the OPC server due to a change in its own Windows configuration. For example, someone may turn on the Windows Firewall, enables Simple File Sharing, or changes the Security Limits of the DCOM access permissions.

 

Repair Procedure

In the case of DCOM error 0x800706BA, first you must check if the OPC server is still running. If the OPC server has shut down, analyze the Trace Viewer logs to find the cause of the unexpected shutdown.

Next, reconnect the OPC client to the server to automatically restart the OPC server. Once the OPC server is connected, ensure that the OPC client application is able to retrieve data using a synchronous method. Specifically, you should attempt to issue a Synchronous Cache Read, or a Synchronous Device Read. As each OPC client application performs these operations in a different way, check with your OPC client application vendor to find out how to perform these types of reads.

 

Add Correct Access Permissions on the OPC Server Computer

Windows uses the COM Security tab to set the system-wide Access Control List (ACL) for all objects.

To add the correct permissions, proceed as follows:

  1. In the Windows search box, enter DCOMCNFG.
  1. Press ENTER.
  • The DCOM configuration process is initiated.
  1. In the Component Services window, under Console Root, expand Component Services, and then expand the Computers folder.
  • My Computer is in the Computers folder.
  1. Right-click My Computer and select Properties.
  1. In the My Computer Properties dialog box, select the COM Security tab.
  1. In the Access Permissions section, click Edit Default.
  1. Add Everyone and select the Local and Remote Access options.
  1. In the Access Permissions section, click Edit Limits.
  1. Add Anonymous Logon and Everyone to the list of Group or user names. Then enable Local and Remote Access options.
  1. In the Launch and Activation Permissions section, click Edit Default.
  1. Add Everyone to the list of Group or user names. Then enable the Local and Remote Launch and Activation options.
  1. In the Launch and Activation Permissions section, click Edit Limits.
  1. Add Everyone to the list of Group or user names. Then enable Local and Remote Launch and Activation options.
  1. Click OK.

 

Turn off Windows Firewall

If the OPC client computer is behind a firewall (hardware or software), callbacks may fail to arrive at their destination. While the OPC client will be able to make outgoing OPC calls, callbacks from the OPC server may be blocked by the firewall. To correct the problem, you need to turn off the firewall.

 

If the computer resides on a safe network, there is usually little potential damage as long as the firewall is turned off for a short period of time. Check with the Network Administrator to ensure it is safe to temporarily turn off the firewall.

 

To turn off the Windows Firewall, do the following:

  1. In the Windows search box on the taskbar, enter Windows Defender Firewall.
  1. Press ENTER.
  1. Select Turn Windows Firewall on or off.
  • The Customize Settings window displays.
  1. Select Turn off Windows Firewall (not recommended).
  1. Click OK.

Once the communication works, ensure that you turn the firewall back on.

 

Add Correct Access Permissions on the OPC Client Computer

To add the correct permissions, proceed as follows:

  1. In the Windows search box, enter DCOMCNFG.
  1. Press ENTER.
  • The DCOM configuration process is initiated.
  1. In the Component Services window, under Console Root, expand Component Services, and then expand the Computers folder.
  • My Computer is in the Computers folder.
  1. Right-click My Computer and select Properties.
  1. In the My Computer Properties dialog box, select the COM Security tab.
  1. In the Access Permissions section, click Edit Limits.
  1. Add Everyone to the list of Group or user names. Then enable the Local and Remote Access options.
  1. Click OK.