I know all the issue so many people have with trying to register an add-in dll, between 32bit/64bit, regasm location, command, running as admin and so on. So, I made a visual tool to do it for you, simply open it, browse to your dll and click Install or Uninstall to register and unregister any SolidWorks Add-in dll.
I've open-sourced the entire code as well, which is well documented if anyone wants it (all my code going forward is 100% open source)
Find the compiled tool here if you just want to run it and try it out Folder Viewer - Fasetto
Find the source code here GitHub - angelsix/solidworks-api: C# SolidWorks API stuff in the Tools folder