'HTTP Error 503. The service is unavailable' message in IIS7 – Application Pools

One of my IIS7 virtual directories wigged out today and started to give me the following error screen.

Service Unavailable – HTTP Error 503. The service is unavailable.

I found a post from Rich Strahl that pointed me in the right direction. When I brought up my Internet Information Services Manager and clicked on Application Pools, my DefaultAppPool was stopped.

Unfortunately, my application pools were already set to auto-start and restarting the application pool didn’t solve my problem. As soon as I tried to bring up my website, the application pool would immediately stop again and give me the same error screen. After spending the next 10 minutes or so restarting Windows 7 and starting and re-staring my application pools to no avail, I decided to re-install my IIS7 and Windows Process Activation Service features.

After re-installing these windows features, everything was back in order. Unfortunately, I did have to add ALL of my virtual directories again, but I expected as much. You can re-install these features from the Programs and Features screen by clicking on Turn Windows features on or off.

On the Windows Features screen, you can uninstall any feature by removing the check next to it and then clicking OK. You can then return to this screen after restarting windows to reinstall them.

Hope this helps someone. If anyone knows how to correct this without reinstalling the features, please comment!