I installed Microsoft Visual Studio 2015 Update 1 which was released in the past few days.
As a developer always has to keep up to date… And quite frankly the original VS2015 RTM was running a bit too unstable for my taste… (compared to VS2013)

However once the installation was finished and I tried to open an existing solution
one error message after another started to pop up:

So I took a look at %UserName%\AppData\Roaming\Microsoft\VisualStudio\14.0\ActivityLog.xml
to get further information and it was full with error messages like this one:
SetSite failed for package [CollaborationPackage][Could not load file or assembly System.Collections.Immutable, Version=1.1.37.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a or one of its dependencies. The located assembly manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)]:{ at Microsoft.VisualStudio.Composition.Resolver..ctor(IAssemblyLoader assemblyLoader)…
…Could not load file or assembly ‚System.Collections.Immutable, Version=1.1.37.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a‘ or one of its dependencies. The located assembly’s manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

After researching on the Internet and asking colleagues I found a few „possible“ bugfixes and I tried them all:

• Recursively deleting all *.msi and *.cab files in the directory c:\ProgramData\Package Cache
  Then reparing the installation.
• Clearing the caches:
  ItemTemplatesCache
  ProjectTemplatesCache
• Running the following commands from an elevated command prompt
  devenv /clearcache
  devenv /updateconfiguration
  devenv /setup
  devenv /ResetSkipPkgs
• Deleting the directory %localappdata%\Microsoft\VisualStudio\14.0

However none of them solved my problem.

So in the end what I did (and what actually worked) was this:

1. Completely uninstall Visual Studio 2015 (plus all external components that I had already integrated into it like TFS PowerTools, …)
2. Deleting the directories
   %localappdata%\Microsoft\VisualStudio\14.0
   %UserProfile%AppData\Roaming\Microsoft\VisualStudio\14.0
   c:\Program Files (x86)\Microsoft Visual Studio 14.0
3. Installing a fresh copy of Visual Studio 2015 with Update 1 (slipstreamed).
4. Installing all of the external components and studio extensions again.

I do realize this was a bit drastic, but it was the only thing that actually worked in the end.

I hope that Microsoft will do a better job with their Visual Studio Updates in the future, as things like this cost a lot of time and nerves…

My guess is, that it may have been caused by some Visual Studio extensions (but they were up to date before update 1). Since Microsoft provides a mechanism to install and maintain extensions, I would also expect them to ensure, that updates do not break this process or Visual Studio altogether. It would be OK if problematic extensions were detected and deleted or disabled. But not installing an update and then getting tons of errors afterwards. That can surely not be the answer…

But at least Visual Studio 2015 Update 1 (once it works) seems to provide more stability when coding and using the editor extensively. So it was at least worth it. 🙂