Good, thank you for letting me know, I am glad that it works now.
I would still be interested in knowing which concrete OPC server are we discussing here.

Best regards

What OPC server are we talking about? (vendor, model).

Normally, all OPC servers appear/should appear in DCOM configuration - even if they do *not* run as Windows service.
Yeah, maybe the in-process servers would not appear, but then, it is unlikely that an in-process server would have a user interface (at least not driven by the same code/in the same process) - and if it did, it would be a bad design choice, because the client can be a Windows service and then the server would also run without a chance to shown a UI.

All in all, there are too many weird things about this setup.

Do you know how to check the server's entries in the registry? From there, we could at least figure out whether it is in-proc or not.

Best regards

Hello,

0xC0040008 corresponds to OPC_E_INVALIDITEMID. It is not generated on the client side: It is the OPC server that is responding with this error.
It is surprising to see this error code come up differently based on the client application (provided that the same Item ID is being used), as the validity and presence of OPC Items IDs (in the server) should not really depend on such things. Therefore, there must be some indirect independence.

One thing to check is how the "Identity" of the OPC server is configured (in DCOM - on the Identity tab of the server properties). What is your setting there?
And, use the Task Manager to look for the server process (on the Details tab), and check a) whether the server runs under the expected account ("User name" column), and b) that you accidentally do not see two or more server processes running (this can happen e.g. when the server's Identity is set to Launching user and programs running under different users are starting it).

Where I am getting with these? Well, the error you are getting looks more like that the OPC server has not actually properly or fully loaded its configuration. And I have seen that happening when it was run under the wrong account, due to permissions, and even configuration (a server might be storing the configuration *per user*).

I do not quite get this part of your post: "Is it possible to disable the auto reconnexion to the server OPC?" - is that an unrelated question? If so, please post it separately.

Best regards