Issue: Visual Studio 2012 > “Unable to launch the IIS Express Web Server”

Steps to Problem/Issue

  • 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

Look for <applicationPools> node.

I updated managedRuntimeVersion=”4.0″ to “4.0.30319”

<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!

Roy Kim