Activer Directory Users cannot login to iMac

Hi,

I have an iMac that is bound to active directory on Windows 2003 SBS. Up until recently active directory users were able to login to the iMac. Also, I followed the MS KB article about the sidestepping the digital signing that Mac clients have a trouble with. Other than that I'm wondering if any one has encountered this problem before or if they have any ideas what might be causing it? Thanks.