An unhandled Microsoft .NET Framework exception occurred in w3wp.exe

I encountered this error while developing a website with web forms in asp.net 4.5.1 I ran it with IIS.
It worked good earlier. Suddenly it threw an exception, when I debugged it. Message was "An unhandled Microsoft .Net Framework exception occured in w3wp.exe [XXXX]"

There were couple of workaround to bring it back to the previous.

Solution 01:
Try running visual studio "As Administrator". If the issue is still there please follow solution 02

Solution 02:
Try to find the message in event viewer something similar to this:

"Description: The process was terminated due to an internal error in the .NET Runtime at IP 6B484BC2 (6B300000) with exit code 80131506."

If it is there, It was caused by updates of .Net Framework 4.5. Try uninstalling last update. It might solved the problem.

You can check event viewer in following path.

Visual Studio > View > Server Explorer > SERVER_NAME > Right click on "Event Log" > Launch Event Viewer > Windows Logs > Setup.

Solution 03:
If the problem still exists, Try installing hot fix from following link:
Unhandled exceptions cause ASP.NET-based applications to quit unexpectedly in the .NET Framework: