Class Not Registered

08 June 2018

I wrote a class which was COM-exposed and registered it using RegAsm. It was a 32-bit library on a 32-bit machine, being called by a 32-bit caller. Yet when the calling program tried to make an instance, it got the error “Class not Registered”.

My Solution

In my case, the error was actually because a dependency of my class was not registered. I registered my dependency and got a different error. In the end, I needed to use a different version of my dependency DLL which other consumers were using, which was pre-registered.

Other things to check

Your class is annotated with ComVisible and a new, unique GUID which you have generated, which is different to your AssemblyGuid in AssemblyInfo (you will get build errors if they are the same)

[ComVisible(true), Guid("20E9E1BF-EC98-4693-BBE3-BB4E0542B52F")]

In Project Properties (in Visual Studio) you have set the following:

• Application -> Assembly Information -> Make assembly COM-visible to true
• Build -> Register for COM interop to true

Further reading

Here is a tragic questioner on TekTips who never got an answer to their identical question.