event 1053 (Userenv)

I keep receiving this error.
event 1053(Userenv) Not enough server storage is available to process this command

Windows 2003 server With SQL 2005
Memory 2Gb
processors 2 Xeon 3.00GHZ
storage C: 18gig 7 gig free
D: 50gig 49.4gig free

When the system starts this error i loose all access to the network but everything locally still works. The only way i have solved it is reboot the server every day at 7:00 am but about 4:00pm it comes back.
i have already tried “increase the Kerberos Token size”

Any one know how to fix this???
Chris