So after installing Visual Studio 2015 Update 2, my Xaml Designer decided to stop working. Every time I open the designer by clicking on a xaml file, it would show an error dialog that says “Visual Studio has encountered an unexpected error.” – not very helpful. Going to the menu, Options > Xaml Designer > General property page would yield an error “An error occurred loading this property page”.
I then tried re-installing Visual Studio 2015. Same issue. I then tried opening Expression Blend, it doesn’t work, but I got a some more interesting clues – it tells me to check ActivityLog.xml – In it, there was a telling error:
SetSite failed for package [XamlDesignerPackage][This access control list is not in canonical form and therefore cannot be modified.
Basically my permissions were corrupted somewhere in some file. I had a hunch. A test by logging on to a fresh Windows user account and opening VS xaml editor confirmed that the issue was limited to my profile account. I tried remove all traces of Visual Studio from profile but removing the obvious AppData folder didn’t fix the issue. There were just too many places it hides files. As a last resort, I reset all permissions on my profile folder such that I was the owner and had write access and surprise! it works!! Now I know what to try next time.