I have an existing application that was written in .NET 3.5. The piece of code in question is using the FileUpload control and its SaveAs method. Its worked perfectly for the past six months, but I've recently upgraded the project to .NET 4.0 and I'm now receiving an "Access to path (...) is denied" every time the method is called. It works fine locally in dev mode but fails on my prod server. I've upgraded the website to run under .NET 4.0 and I've made sure the account (Network Service) it runs under in the app pool has full control. Other than upgrading to .NET 4.0, nothing has changed for the project. Any ideas or suggestions? Thanks in advance.