Server Application Unavailable

Is there any error more annoying in .net web development? I hate this error because it's so unhelpful. I actually got this error today and it took me a while to track down what the issue was thanks to that rubbish error message being returned to me.

One of the guys inside in work setup the project for me for a new website but never changed the .net settings from the default asp.net 2 runtime to the asp.net 4 runtime. "No problem" I thought and I quickly updated the runtime from .net 2 to .net 4 using my handy command.

I double checked IIS6 and confirmed that the new runtime was in effect. However, every time I tried to load the website I was seeing the 'Server Application Unavailable' error message. I checked the Event logs and nothing was mentioned in there so that was no help. I double checked all the settings and everything seemed correct.

Then it hit me. I had updated the framework but not refreshed the application pool for this website. Sure enough, once I refreshed the application pool the site came to life. I just wish IIS had some better error messages to help work around these situations. A simple prompt telling me that the application pool runtime wasn't matching the website runtime would have pointed me in the right direction.

Ah well, at least I know in future it this happens again :)