Can I run an ASP.NET 3.5 application on a server with ASP.NET 4.0 installed without any problems? I am hosting a large number of website on a Godaddy server with ASP.Net 2.0/3.0/3.5 installed. However, my newest application needs 4.0 to run. If I upgrade the server to 4.0, will all my other sites break?