I was working with a customer today that, after upgrading to the latest version of our software, was running into an error that I had never seen before.  The product, as you may be aware, is a web-based Product Configurator for Microsoft CRM.  Historically, our upgrades have been very clean and easy, but today the customer received the following error message when attempting to launch the application:

The file or directory is corrupted and unreadable.

The error was occurring at launch (during the initialization of ASP.NET) and was caused by an IOException.  Inspecting the call stack it was apparent that it was happening during the System.Web.HttpRuntime.FirstRequestInit() method while loading the assemblies from the \bin folder (System.Web.HttpRuntime.PreloadAssembliesFromBin() method).

My first thought was that something security-wise was amiss.  So, via Windows Explorer, we inspected the security properties on the folder for the website.  Sure enough, some credentials were messed up so we fixed those; but the application continued to fail with the same error.

Something in the back of my mind told me it was still security related.  After considering it a bit the answer was obvious.  We proceeded to open \Windows\Microsoft.NET\Framework\vX.X.X\Temporary ASP.NET Files to the folder for the application.  Upon drilling down the folder tree Windows reported the exact same error.

To fix it, all we had to do was fix the security settings on the folder, perform a CHKDSK, and delete the application's folder in the \Temporary ASP.NET Files folder.  After that, everything ran beautifully.