Hi Tristan,
This forum is to discuss the Open Specifications documentation.
I would suggest you post your question in the following forum in order to receive more accurate assistance:
Directory Services

Discussion on Windows Server Active Directory services
http://social.technet.microsoft.com/Forums/en-US/winserverDS/threads/Just as a quick check, make sure that your client and that your server do not have a difference in time of over 5 minutes. Sometimes, the times look similar, but they are set to different time zones.
By default, AD requires the time to be within 5 minutes but tat can be configured.
I sure you'll find the help that you need on the forum that I'm pointing you to.
Thanks and regards,
SEBASTIAN CANEVARI - MSFT
Senior SEE Protocol Documentation Team