I've been trying to resolve this issue for months, I completely uninstalled and reinstalled, repaired Visual Studio to no avail and get the same results.
I get this exception in debug:
An unhandled exception of type
Microsoft.VisualStudio.Composition.CompositionFailedException occurred in Microsoft.CodeAnalysis.Workspaces.dll
An exception was thrown while initializing part "Microsoft.VisualStudio.LanguageServices.Implementation.TaskList.CommentTaskTokenSerializer".
removing/renaming folders in %appdata%.
I have figured it out.
Turns out access was being denied to a registry key.
Using Sysinternals Software Process Monitor I was able to see the key that was reporting ACCESS DENIED.
Process Monitor is a tool you can download for free.
I also Used PSTOOLS from Sysinternals Software for free to get the highest permissions possible for RegEdit. RegEdit alone would not let me change the Permissions for some reason.
I stumbled upon a different fix for VB6 and then decide to see if a similar issue was happening with Visual Studio, As I suspected it was denied registry access.
I set the permissions on the registry key to Full Control for my username, Everything is great and works now :)
FOLLOW THIS GUIDE, but use devenv.exe in the process monitor filter. TIP: Process monitor filters can be a bit confusing, its best to use IS NOT and then EXCLUDE when setting up filters for Process monitor so the result set only shows the desired results EX: Process Name, Is Not, devene.exe, Exclude then click add.
The explaination on the filters in the guide is ok but this method is much clearer.