SIMs user not recognised

[TomFishwick]

*Pops head up from behind the shadows*

Forum lurker here, I don't post because most of the time others have asked the question and gotten an answer already!

Only this time something's come up that has me (and the boss) confused. We have one member of staff that can't logon to SIMs.

Now with every other member of staff they use windows credentials. Select Current Windows User and away they go

 

That doesn't happen with this user. Comes back with the good ol' "Invalid username/password" error. 

 

Only it's not. I've gone through his account in AD with a fine toothcomb, checked his user account in SIMs user manager and compared it to other accounts. Everything matches up perfectly. Only SIMs doesn't recognise the user or password.
We tried deactivating and reactivating the account with SIMs to trigger it working again. No such luck.

As a last ditch effort we changed his AD password, no luck. Finally we created a SIMs username and Password manually and would you believe that did work!

 

It's an ugly work around though and all other staff can just sail on by with Windows User.

Anyone have any ideas as to why just one user would have this trouble?