Came across this error today:

HTTP Error 500.0 – Internal Server Error C:\PHP\php-cgi.exe – The FastCGI process exited unexpectedly

I was working on a Windows Server 2012 R2 with IIS installed.

After installing PHP 5.6 the error occured when trying to access any php files.
So apparently you need VC++ 11 runtime for PHP 5.5 or newer.
the solution was quick, download, install and iisreset (http://www.microsoft.com/en-us/download/details.aspx?id=30679)

Make sure you download and install the x86 version (vcredist_x86.exe), PHP on Windows isn’t 64 bit yet.

If you’re running PHP 5.4.x then you need to install the VC++9 runtime (http://www.microsoft.com/en-us/download/details.aspx?id=5582)