I've run-up against an interesting problem on our network. We are running a Windows Server 2008 R2 environment with primarily Windows 7 clients. Earlier this week, we lost our Internet connection but I seriously doubt that has anything to do with what we're experiencing now.
Users began reporting they were unable to open Outlook. They continuously received the error "server is unavailable." Oddly enough, yesterday, I was able to delete and recreate their Outlook profile which seemed to fix the problem. This morning, they are experiencing the same issue again but this time, recreating the profile isn't fixing the problem. I've been forced to set them all up with OWA which, understandably, they're pretty upset with.
We're also using a CRM application which uses AD accounts to authenticate to a SQL database. That has seemed to stop working as well. If I change their authentication to SQL, it works fine.
There appears to be some kind of authentication issue but I'm not quite sure. I thought I'd put this out here and see if anyone else has run across this type of problem.
1) Outlook client will not work but Internet-based (OWA) solution, along with all cell phones, work fine
2) AD authentication to SQL isn't working but SQL authentication does.