VS 2012 Express unable to launch IIS Express Web server

I installed Visual Studio 2012 RTM.
Created an MVC 4 project template in Visual Studio 2012
Without any code changes, I hit F5 debug.
Issue: I get a pop up message ”Unable to launch the IIS Express Web Serve“

After much searching and many suggest re-install Visual Studio 2012, but it takes a long time (>20 mins) and I’m pretty stubborn at times to find root cause.

I found myself looking at the applicationhost.config file located at
C:\Users\<username>\Documents\IISExpress\config

Look for <applicationPools> node.

I updated managedRuntimeVersion=”4.0″ to “4.0.30319″

Example:
<applicationPools>
<add name=”Clr4IntegratedAppPool” managedRuntimeVersion=”v4.0.30319″ managedPipelineMode=”Integrated”     CLRConfigFile=”%IIS_USER_HOME%\config\aspnet.config” autoStart=”true” />

Back to Visual Studio 2012 Project Solution, I hit F5 Debug and IE loaded with the App!