Hi.
I was able to reproduce what you are seeing.

However, while the symptoms are quite similar as before, the cause of the problem is now different. What happens is that the assembly references in the project file are mixed up, and that causes the App_Web* assemblies to be not found.

There are multiple issues in the project file (WIN_TEST.csproj), e.g. there is:

- this has an incorrect version/build number (5.62.456.1) compared to what the other assemblies have (5.62.1032.1), and in addition it leads to a path that's not inside the solution zip file.


When App_Web* assemblies are not found on the main thread (with lines 48-49 in Program.cs) present, it throws the exception you reported, and the whole program crashes.

When lines 49-49 in program.cs are commented out, the "not found" error then happens inside the task. In this case, unfortunately, it gets swallowed up and nothing is reported. So, the program is actually not "stuck" in "_easyDaClient.EventingFailure += OnEasyOpcDaEventingFailure;". It has thrown an exception there.

You can verify that this is the case by placing a breakpoint into the "catch" block of StartClient(), and inspecting the exception object ("ex").

Remedy:
1. In the project References, do "Manage NuGet Packages", and remove the OpcLabs.QuickOpc package
2. In the project References, remove any remaining OPC Data Clients assemblies. Specifically, remove the App_Web* assemblies.
3. In the project References, do "Manage NuGet Packages", and add the OpcLabs.QuickOpc package.

Note that when I first received your solution, I had removed the assembly references and replaced them with those that work on my system, without realizing that wrong assembly references can themselves be the cause. But the issue with BoxedApp exists as well I believe.

Best regards

Hello,
no, no changes to the original C# code should be needed, just the app.config modification.

In my test, adding the <appSettings> part - which looks like yours in the picture - resolves the issue with the original code reliably.

Please send the current state of you solution so that I can check that we have the same thing.

Best regards

Hello,

your mention of boxedApp has triggered my suspicion. I think it is actually the cause the problem (sorry, Microsoft, for blaming you prematurely). I am fighting with this library quite a lot. It is used to make the deployment easier - so that users don't have to deploy things like OPC Core Components, Visual C++ libraries, or OPC UA Certificate Generator. Which is good, but it apparently has problems in some situations.

With knowing this, I was able to get the problems go away by following the instructions here: kb.opclabs.com/How_to_disable_prerequisites_boxing (basically, copy the section from the snippet at the bottom of the page, and paste it appropriately into project's app.config in Visual Studio.

In some cases (but not so often, because many users already have them) it may then be necessary to install the actually prerequisites the BoxedApp was meant to provide:
opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...ml#Prerequisites%20Boxing.html

Best regards

Hello.

Thank you, I was able to reproduce the issue using your solution. And, the key is in the call stack you also provided - there, it can be seen that the program has blocked itself when trying to load one of the assemblies we have for OPC Classic.

However, I have very high confidence (although not 100% certainty) that there is nothing wrong in user's code, or our code. It looks like Microsoft problem. There is nothing else than simply loading that assembly (dynamically) inside the queued Task. This should work.

Since these are "mixed-mode" assemblies (with native code) that are rarely used, I would not be surprised that there was some problem inside MS part that has not been discovered yet.

Given this, I can only provide workarounds. I tried two of them, and there may be more:

1) Trigger loading of the mixed-mode assembly at least once BEFORE it would get loaded from inside the Task, e.g.:

OR

2) Switch to fully managed code implementation of OPC Classic client part (slight behavior differences may exist between the two implementation):

Best regards

Hello.

There are some concerns that have to do STA/MTA threads and SynchronizationContext, but before we get to explaining that (and sometimes that gets complicated and I do not pretend to fully understand all of it either), do you have a reproducible project (possibly the console one, for start) for me to look at?

Thank you