iis 7.5 - IIS 7.5 pass through authentication fails on UNC share websites

I have a site which fails to authenticate using windows authentication now it has moved to IIS 7.5.

The site is:

On a UNC share
Using windows authentication

Has a custom app pool Id (domain account) IIS 7.5

Everything runs fine if it is not on a UNC share. This site used to run fine on the previous IIS 7 server with all the same settings apart from being on a UNC share.

I have set the unc with caspol to be:

1.6. Url - file://\fileserver\websites*: FullTrust (Exclusive)

The app pool identity has all the right privileges and is used to run app pools which have no windows authorisation but use forms auth instead, and these work fine on UNC shares.

Please if anyone has any ideas it would be great to hear them.

Thanks in advance.

Answer

OK so I have found the solution:

The IIS Server needed delegation permissions to be set in AD.

See this article on MSDN:

http://msdn.microsoft.com/en-us/library/ms998355.aspx