Error message 'Value cannot be null. Parameter name: userContext' in Visual Studio 2017
I had same problem to. My solution is quite similar from Tahir Hassan.
Go to ...AppData\Local\Microsoft\VisualStudio\15.0...\ delete the file
"privateregistry.user.bin"
Start Visual Studio -> VS only ask to sign in or not.
You don't have to download any updates after that.
I had this problem. Close VS, go to %LOCALAPPDATA%\Microsoft\VisualStudio\
and delete/rename a folder whose name starts with 15.0_
.
Then start Visual Studio, then download and install the latest update.
After that it should work - Best of luck.