AD accounts that have been set up to never expire are expiring

Hi,

We have a mix of 2003/2008 R2 DC's. We are experiencing the following issue :

AD accounts that have been set up to never expire are expiring. Seems that users were contractors now permanent or are contractors. When looking at these accounts on the "account" tab on AD the account is showing to expire on the 24/1/2013 Although expiry is ticked to "never" and the date is greyed out, it seems as though it has still
used this date to expire. Users are getting an error message when logging into the PC "Account has expired".

Cheers

HA