if you know the account name use account lockout tools from microsoft to see if its stuck on a pc or server anywhere,
http://www.microsoft.com/en-gb/download/details.aspx?id=18465
Is the account still in AD or is it a local account within VMware?
I also presume you've checked the session manager in vcenter?
If the account is still logged into a host i believe that stays there until the host is rebooted but may be wrong...maybe someone else could confirm that or Google 
Hope that helps
Alex