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Invalid class string (0x800401F3 (CO_E_CLASSSTRING)) when reading remote item.

08 Dec 2021 14:09 #10441 by support
Thank you for update.

Yes, missing or unreachable OPCEnum could have been the cause for the original problem.

You do not need "additional information" to do subscribe (well, you need update rate etc., but that's all always there). But, it is not uncommon that Read works and Subscribe does not. The reason for that is that for Subscribe to work, the server must be able to call back to the client, which means that DCOM must also be configured to allow this.


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08 Dec 2021 10:04 #10438 by Alvar Ljungfjär
Okay, I did some configuration to local policies as well as added a TCP endpoint to OPCEnum service which was missing. So the problem I had must have been my opc configuration.

Now it seems like I can read specific items, but when I subscribe to items I still get an error (different error mesage than this thread which says error can be DCOM or locally related). I will open a new thread about that error but before that I want to make sure I don't need additional configuration for subscribing to items as opposed to just reading items.

Best regards!

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08 Dec 2021 07:35 - 08 Dec 2021 09:36 #10436 by Alvar Ljungfjär

I am setting up an opc classic DCOM communication between two machines in the same domain. On remote machine: First I am browsing the servers using the opc server machine's IP adress and I recieve the correct result, then I am using that ProgId/server class to read an item on the targeted machine and server class, like this:
vtq = Client.ReadItem("",  "Kepware.KEPServerEX.V6", "[itemId]")
This ends up throwing this error
Invalid class string (0x800401F3 (CO_E_CLASSSTRING))

When I execute this code locally on the opc server I successfully get the value of the item. I wonder if the error is missrepresenting and that the actual problem lies in my DCOM configuration on the machines. If that is not the case I am missing something else, any help is appreciated. :)

Edit: Firewalls has been disabled.

Best regards!
Last edit: 08 Dec 2021 09:36 by Alvar Ljungfjär.

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