IIS 7.5 and MVC 3 using Windows Authentication - Getting 401 for static content, but never get prompted for credentials

Question

I have a MVC 3 site running on Server 2008 R2 with IIS 7.5. I am wondering why, (using fiddler), I keep getting 401 responses on static content followed immediately by either a 302 or a 200? Is this something I need to be concerned about? I can directly navigate in my browser to the content giving a 401, and the browser displays it without prompting for credentials.

If I do a trace on failed requests, I get this as output:

ModuleName UrlAuthorization 
Notification 4 
HttpStatus 401 
HttpReason Unauthorized 
HttpSubStatus 0 
ErrorCode 0 
ConfigExceptionInfo  
Notification AUTHORIZE_REQUEST 
ErrorCode The operation completed successfully. (0x0) 

I have checked all the directories, and files and they have the application pool user, (domain user), as owner with full permissions.

As I said, my site is not broken, but I am wondering if I have an issue with my set up.

Thanks in advance.

EDIT: Here is a sample from Fiddler:

Answer 1

Alright ... I resolved this in an odd way. In IIS 7.5 you can set the credentials to use when accessing the physical path for the file system. It appears by default it uses a "pass through" option ... somehow this appears to not work even when IUSR has access on the file system. I made a basic user account, granted them read on the file system, and then under IIS -> my website [Right Click] -> "Manage Website" -> "Advanced Settings" and updated the Physical Path Credentials.

Oddly, Orchard, sharepoint, tfs, and SSRS websites on the same server didn't have this issue ... just my MVC3 app running from wwwroot.