I have found the solution and it all has to due with the MaxtTokenSize registry key. Please read the MS Article http://support.microsoft.com/?kbid=327825. 

There are a few other posts here that  have...

I am experiencing the same problem.  Can you count the number of Global groups the user trying to connect is a member of.  I am thinking it might have something...

Further to my Post - Could it be a result of the users being a member of too many AD Global groups???  The Sec Admin users have considerably more group...