I have an application that works great on my development workstation but fails when the application is deployed to the live environment. It seems that Application_Start is not being called in the live environment.
I was able to fix it by removing the PrecompiledApp.config file that was in the root directory of the web site on our test server. I'm guessing that file was a holdover from when the project was a Web Site project. I recently converted it over to a Web App project. So if you are building a Web App project, make sure you DON'T have a PrecompiledApp.config file on your target server.