That's great. I am glad you have found the cause.

Best regards

Sorry - so in fact it is not working yet?

Is the version in GAC also 5.23.1225.1 ?

Note: the very recent build (the one on the Web) of version 5.23 is 5.23.1371.1. However it is fine to work with an older one - as long it is the same both on the development computer and on the target computer.

Also, look at the "Precise Version" attribute on the references in your Visual Studio project. If it is "true", which I think will come as default, then the app must find the assemblies of the precise version as used during the build. You can set it to "false" to allow for loose version number checking.

I am glad you resolved it.

But, I do not fully understand the description - can you please provide details? Specifically, is there anything on our side that we either did wrong, or at least could have done better (to prevent such errors)?

Thank you

Installing into the GAC should be done using the GACUTIL utility. I am not sure if your method works.

Note that version 5.23 also needs Microsoft.Contracts.dll, i.e. not just everything that starts with "OPCLabs". I had a long exchange with a customer who insisted that all assemblies are installed, whereas in the end this particular one was missing.

Are there any details to the exception? No precise file indicated? Does it have InnerException?

Does the server have .NET Framework 3.5 installed? (if it has SP1 for the operating system, it will have it automatically, otherwise it's not guaranteed).

Have you deployed all the QuickOPC assemblies? On the development computer, they are in the GAC, and therefore Visual Studio does not copy them alongside the executables.

On the target computer, the QuickOPC assemblies need to be either in the GAC again, or in one of the codebase directories - usually, in the same directory as the .EXE of the app.