I have an IIS 7.5 (Win2k8R2) Webserver, which publishes an UNC Share (on a Fileserver) with restricted access. The AppPool Identity is a Domain User-Account with read access to mentioned UNC path. Authentication modes are set to Anonymous and Integration Authentication.

When I access the path via localhost from the Webserver itself, it works, but if I try the Hostname or IP from either the Webserver or a Client, I get three authentication prompts (does not accept my credentials) and a 401.3 Unauthorized error message (but it states that I am logged in as my normal credentials which definitely have access rights to the UNC path and its files). Security Zone is set to Local Intranet. Sysiniternals Process Monitor lists CreateFile operations on the UNC path (and other existing files in it) with Access Denied and Impersonating on the correct credentials.

I don't understand why it is not working, it seems to use the correct credentials on every step on the way but fails with is operations.