We use MVC controllers that access System.File.IO in our application and they work fine in localhost (IIS 6.0-based Cassini). Deploying to IIS7, we have problems getting the controllers to work because they throw UnauthorizedAccessExceptions.

We have done the following to try to resolve the issue: - Set NETWORK SERVICE and IUSR accounts to have permission on the files and folders in question - Ensured the App Pool is running under NETWORK SERVICE and loading the user profile - Application is running under full trust - We tried adding impersonation to web.config and giving NETWORK SERVICE write permissions

Now, we alternate between getting UnauthorizedAccessException and an IIS7 404 page that suggests the routes are being ignored completely (for example we serve "/favicon.ico" via a controller when the physical file actually lives at /content/images/favicon.ico). We used ProcessMonitor to try to track down the issue but weren't successful.