Will upgrade of .net framework from 3 to 4 will shut down all the applications running in .net 3.0.? I had the server in which we have hosted some applications in IIS. But what i have seen is due to upgrade of framework all applications were stopped. Was that correct?
You can run .NET 3.0 and 4.0 applications side-by-side.
However, as you bring .NET 4.0 applications online, you will need to configure the website to use 4.0 and also set any apps running 4.0 to run in a different Application Pool. (This may be why the old ones were stopped.)