Received the strangest case on my desk today. A user was unable to sing in to the internal SharePoint site. When the user tried to logon via UAG everything worked fine.
On the SP server quickly found a lot of these events.
Account For Which Logon Failed: Security ID: NULL SID Account Name: Username Account Domain: Domain Failure Information: Failure Reason: An Error occured during Logon. Status: 0xc000006d Sub Status: 0xc000006d
Binging that did not help much, so I turned to my Security log from the domain controllers, and found a much more helping event.
There it was, the event stated that the credentials was invalid.
The computer attempted to validate the credentials for an account. Authentication Package: WDigest Logon Account: Username Source Workstation: SomeServerName Error Code: 0xc000006a
Strange, as the user was both able to logon via UAG and start a VPN connection. Well, trust the DC I thought, and opened ADUC and reset the users password to the same password as before and guess what? It worked!!
How this is possible, I do not now, but if I find the time, I will for sure dig into it.