Middle Tier - ISAPI Filter Not Authorised

[waless]

We are experiencing a strange issue with two of our Middle Tier Servers, these are new built but both have the same issue. When clients authenticate across the servers the Middle Tier authentication fails at the server end with a IIS error.

HTTP Error 401.4: Unauthorized: Auhtorization failed by filter

This occurs when the client reboots and authentication takes place, Middle Tier then fails.

Any suggestions or ideas appreciated.