They are certainly two different errors.

To the first one reported, 0xC0040201: I still do not know what is its InnerException. But anyway, the particular error code does not come From QuickOPC. It is likely that it comes from the OCP Server itself, so you need to ask at their side.

To the second one reported,0x800401F3: In English Windows, this is "Invalid class string", an error code predefined by Microsoft. It is meant to indicate that the ProgID you are using ("FactoryTalk Gateway") is not correctly formed, but it can also mean that the server is not properly registered. Check whether the ProgId is right. In addition, have a look at whether your application in running in 32-bit or 64-bit process: In some situations, servers register themselves correctly only for 32-bit usage. .NET programs (when build for AnyCPU target) run, by default, in 32-bit process on 32-bit Windows and in 64-bit process on 64-bit process. It is not uncommon to encounter problems with old OPC servers when trying o access them from 64-bit process.


Regards

You are confusing things. The screenshot you have sent now is for different error than originally reported.
Which one is the right one?

Is it really "Class string not valid", or is it "Invalid class string"?

Hello,

the error message refers you to details in the InnerException property.
What is the InnerException then?

Regards