Ever since we've installed .NET 4.0 and ASP.NET MVC 3 on our IIS servers and we deploy our websites we get an "Server Application Unavailable".
There are no logs in the eventlog regarding the problem.
We think it is related to the installation of .NET 4.0 or MVC 3.0 as we've seen this happen through each stage of our deployment. We first upgraded our DEVelopment environment, then our ACCeptation and now finally we are seeing the same behaviour in our PRoDuction environment.
Recycling the application pool of the specific web application solves the problem.
We did not have this before, and are wondering what the installation of MVC 3.0 or .NET 4.0 could have changed. All our webservers run on IIS6.
Update 12-08-2011
We've noticed something else: When we have one application pool running three .NET 4 applications. And we change a value in the web.config of one of those applications, which should cause it to recycle, only this application no longer works, the other two are still running fine. Meaning that an automatic recycle never happens when a file changes inside the web application.
Best Answer
Is there more than one application in your troublesome App Pool? If so, try separating into different pools as this could be causing the problem - especially if the two applications use different versions of .Net.