Server Application Unavailable Message

If you have ever received an error message on a .Net application that simply stated "Server Application Unavailable" you might find this useful.
When you receive this error, make sure to check the event viewer on the server. This is found under administrative tools. Under the application event log, you will likely find an error that states: "It is not possible to run two different versions of ASP.NET in the same IIS process. Please use the IIS Administration tool to run the application in a separate process."
An application pool is a process that responds to web requests under IIS. An application pool does not have a setting for what type of ASP.Net applications will be run in it. Instead, it loads the appropriate libraries when an ASP.Net application is loaded in the process. Because the libraries for ASP.Net 1.1 and ASP.Net 2.0 are similar, but not the same, the application pool cannot respond to requests for both types of applications at the same time. This can cause sporadic behaviour if you are using the server at the same time as another developer and you have applications using different versions of the framework in the same application pool.
Make sure that on your server there is an application pool dedicated to ASP.Net 2.0 applications and one for ASP.Net 1.1 applications. When you add an ASP.Net application to the server, make sure you select the right application pool for it.

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