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Communications Problem when Connecting with Another OPC Client


Last Update: 11/12/2018

Problem:
Some clients may encounter a communications problem when connecting to OPC servers that support more than one version of OPC. Symptoms of a problem include write transaction failure and/or incomplete data change events.

For example, a user is running the OPC Quick Client on the same PC and under the same user account as the production client. When an attempt is made to connect the OPC Quick Client to the server, the OPC Quick Client reports "Failed to connect to 2.0 data access interface." This means that DCOM security may not be allowing callbacks from the server to reach the client, thus causing symptoms similar to those described above.

Solution:
Ensure that DCOM security has been configured properly. For information on configuring DCOM, refer to the Remote OPC DA Quick Start Guide (DCOM). For information on more advanced settings, refer to DCOM - Secure by Default. If connection problems persist after DCOM security has been set properly, do the following:

  1. In KEPServerEX, click File | Project Properties. Then, select OPC DA Settings.
  2. Next, uncheck the Enable OPC 2.0 data access interfaces and Enable OPC 3.0 data access interfaces options. Do not disable all of the interfaces.
  3. Once finished, click OK.
  4. Next, click Runtime | Reinitialize. This forces the client to disconnect, which is necessary for the options to take effect.

Note: If the problem continues, disable a different set of data access interfaces. By disabling OPC DA interfaces that the client can't properly use to communicate to the server, the client is forced to resort to another interface (like OPC 1.0, when using the instructions provided above).

Tags
DCOM

Related Products
KEPServerEX

Related Protocols
OPC Data Access (DA)