Visual Studio Error: “Object reference not set to

I have a weird behavior of Visual Studio 2013 (and 2010), that i cant seem to fix.

I know this is not directly related to programming (similar questions achieve the same error message via code, so i assume it is code within VisualStudio that has a problem).

My projects are C++.

Whenever i click on a project and open its properties, i get the following error box:

with the text:

Object reference not set to an instance of an object.

I can trigger that error message by selecting "Configuration Properties -> General". The view then does not show the information for "General".

My setting is the following: Windows 7 Enterprise SP1 64bit, Visual Studio 2010 (i need the compiler) and Visual Studio 2013 Professional (Update 4).

I have to work with these extensions:

IBM Clearcase Integration
IBM RTC VS Integration
Visual Assist X
Xoreax Incredibuild

What i did try without success:

Remove all VS related files/folders in
- %APPDATA%\..\Local\Microsoft
- %APPDATA%\..\Roaming\Microsoft
- %PROGRAMFILES%
- %PROGRAMFILES(X86)%
- %USERPROFILE%\Documents
Repair/Reinstall VS2010 and VS2013 (i always installed VS2010 first)
Reinstall .NET Framework 4.5.2
Create a new project from within VS2013, i get the usual error plus:
Use TotalUninstaller as described here to remove all extensions
Hooking into the devenv process with WinDBG did not work (in non-invasive i couldnt get it to run)
Start devenv.exe with safemode and log
Uninstall NuGet as proposed here
Create new solution and delete old .suo and .sdf files
Look at output of ProcMon while triggering the error. I checked the registry for that key: nonexistent
Look at logfile at %APPDATA%\..\Roaming\Microsoft\VisualStudio\12.0\ActivityLog.xml generated via /log: the keys are found within other keys of the value "(Default)". No clue on how to interpret that
Reset all user settings via the (also secret) options named here
Run .NET Fixing Tools and SFC
Clean (remove from) registry
- HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\
- HKEY_LOCAL_MACHINE\Software\Microsoft\VisualStudio\

So my questions are

How could i further debug the problem
How can i really delete/reset all user settings and files and cleanup the registry
Could this be related to solutions or projects
Any third party components known to be problematic? .Net Frameworks?