BIS, SBS08 & W3SVC not authenticating

My apologies if this is in the wrong area.

I am having an issue with BIS and SBS 2008 having authentication issues. Through (Telstra) BIS, it continually fails the authentication stating bad password.

However when I restart the W3SVC "World Wide Web Publishing Service" and its dependant service - authentication succeeds and can send receive.

However a few - or anywhere between 3-6 hours later, BIS is reported to have failed and the authentication is invalid. Again if I restart W3SVC it works.

However I cannot seem to find to root of this problem as no Event Logs are recorded and no failures "seem" to occur on the server with anything to do with Exchange or IIS.

Any help would be greatly apprecaited.