Microsoft Visual Studio 15.9 Known Issue
Since Visual Studio 15.9, many users of the IDE, including us, are experiencing issues seemingly related to manifest generation.
Symptoms include errors like the following at build time:
Task 'GenerateAppxManifest' failed. An item with the same key has already been added
They also include runtime exceptions such as the following:
System.Runtime.InteropServices.COMException: 'Class not registered'
System.Exception: Class not registered
The only known workaround at this time is to rebuild the application. However, if possible, we recommend downgrading to the latest 15.8 release until Microsoft releases a fix for this issue. We are working with Microsoft on this and hope that there will be a fix soon.