Why my ASP.NET application broke after a migration?

Question

My web application worked very well in a Windows Server 2003 with .NET Framework 2.0. When I migrated to Windows Server 2008 with .NET Framework 3.5.

With the same code running in both servers the difference between them was the following: for a given async ASHX (IHttpAsyncHandler) the previous server automatically answered the request with the Connection and Content-Length headers. As the new server didn't automatically generated those headers with the previous code, I had to alter the code to do it manually, or otherwise the web clients couldn't determine the end of the response.

My question is, isn't .NET Framework 3.5 supposed to maintain full backwards compatibility with .NET 2.0?

Answer 1

Set the ApplicationPool mode to Classic.

Answer 2

The problem isn't the .Net Framework it's the different between IIS7 and IIS6. As leppie stated you need to set the application pool to classic mode.