We are running a sharepoint site with a subsite for our telephone directory. The sites are hosted on servers within our London domain. We have users in multiple domains accross our network who access these sites. Up until a week ago this was working correctly however we are now getting an error accessing the subsite for anyone outside the London Domain. When trying to access the subsite from a computer on a different doimain (e.g. Leeds), the user is prompted for their username and password which is fine. However after entering their details they get either an error 500 page cannot be displayed, or if using firefox they get a simple line of text saying "No Authority could be contacted for authentication". If within sharepoint we login as a different user and use credentials for the lodon domain the subsite page displays without any errors. We had assumed that this was a problem with the credentials for users outside of London however, if we use a computer on the London domain, load the sharepoint site and login with a Leeds domain users credentials, the subsite works absolutely fine. So the problem only seems to exist when trying to access the site from a computer on a different domain. Very stuck on this so any help would be greatly appreciated. If you need any further information please let me know. Thanks Steve