Hello,

the error you are getting ("Item not in callback. The OPC callback does not contain an entry for an expected item. Most likely this error indicates an implementation bug in the OPC server.") is different from what was reported here in the original post, and the cause and resolution are also different.

This error is not related to DCOM or lower communication layers. Changing DCOM or firewall configuration is not going to resolve it.

The error cause is explained in the message itself. Most likely, the OPC server violates the OPC DA specification by sending back a result which does not contain or does properly identify the items it should have.

The reason it "works" in Connection Explorer is because you are not doing the same thing. In the screenshot from the Connection Explorer you provided, you are actually getting the Value property of the OPC item. This operation is *different* from reading the item.

Given that the likely bug in the server has to do with asynchronous Read-s, I can think of two workarounds for you:

1. Instruct QuickOPC to use synchronous OPC read. Example:

 

// This example shows how to read an item synchronously, and display its value, timestamp and quality.

 

using System;

using OpcLabs.EasyOpc.DataAccess;

using OpcLabs.EasyOpc.OperationModel;

 

namespace DocExamples.DataAccess._EasyDAClient

{

  partial class ReadItem

  {

    public static void Synchronous()

    {

      // Instantiate the client object.

      var client = new EasyDAClient();

 

      // Specify that only synchronous method is allowed. By default, both synchronous and asynchronous methods are

      // allowed, and the component picks a suitable method automatically. Disallowing asynchronous method leaves

      // only the synchronous method available for selection.

      client.InstanceParameters.Mode.AllowAsynchronousMethod = false;

 

      DAVtq vtq;

      try

      {

        vtq = client.ReadItem("", "OPCLabs.KitServer.2", "Simulation.Random");

      }

      catch (OpcException opcException)

      {

        Console.WriteLine("*** Failure: {0}", opcException.GetBaseException().Message);

        return;

      }

 

      Console.WriteLine("Vtq: {0}", vtq);

    }

  }

}

 

2. Change your code from using ReadItem to GetPropertyValue. An example for it is here: opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...%20of%20single%20property.html . Use DAPropertyIds.Value as the 3rd argument, if you want to get the value. This is quite inefficient, and if you also wanted to get other properties (such as timestamp), you run a risk that they will be out of sync with the value.

Best regards

Hello.

Please see opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...ultiple%20Implementations.html .

Apparently the Native implementation has some problem coping with your configuration. I do not know the precise reason for that.

This can be changed from the code as well (see the link); or externally to an application with a config file.

Best regards

Hello.
Thank you for the version information. We need to gather some more, and try out some things.

Can you please:

1. Check Windows event logs if there are any interesting entries *at the time of the error*? That is, open the Windows Event Viewer, and check the entries that appear after selecting Event Viewer (Local) -> Windows Logs -> Application, and also Event Viewer (Local) -> Windows Logs -> Security and Event Viewer (Local) -> Windows Logs -> System .

2. Use the Connectivity Explorer application that ships with QuickOPC to try to connect to your OPC server. It probably will not work (same issue), but we need it in further steps because it allows to configure various QuickOPC parameters. Assuming that it also does not work, report here whether it gives the *same* error as your previous attempts, or something different (what?).

3. In the Connectivity Explorer, select Tools -> Configure Connectivity, then OPC DA ... -> Instance Parameters -> Enable Native Client. Change its value from True to False, and press OK. Then do File > Exit, start the Connectivity Explorer again, and re-do your test with your OPC server. Does it work now? If not, what are the symptoms?

Regards

Which QuickOPC version are you using please?