Unhandled exception - Sheet Manager

When trying to use Sheet Manager you are getting an Unhandled exception with this message.

"An item with the same key has already been added"

Solutuon:

The reason why you get this message is duplicates on "Viewname" in your project. You may not have this in Revit if you create views yourself. If you create Assemblies, Revit can create several views with the same name.

Please make sure to remove any duplicates on Viewname and run Sheet Manager Agian.