What kind of add-in are you attempting to add? It looks like it’s having trouble verifying that your DLL implements the IEdmAddIn5 class. I believe I’ve run into this before but I can’t remember exactly what caused it.
Have you made sure your add-in has “Prefer 32-bit” unchecked?
Your reference DLLs are set to “Imbed Interop Types” = False?
Not sure what else to check at the moment but those should give you a good start.
Have you verified that the add-in can load via the Administration tool the standard way?
If possible, could you attach your project for one of us to take a look at?
There is a billion thing that could trigger that. It’s mainly because there is no dll in the file selection you made that implements the IEdmAddin5 interface.
Either paste our code here or create an MVP repo on GitHub so we can help you
I’m able to get it to add to the vault normally, as in right-click Add-ins in the Administration tool and select New Add-in. Does this work for you? I’m trying to figure out if your add in is not working or if your add-in installer is not working.