Error occurred during logon Event ID 537

Logon Failure:
Reason: An error occurred during logon
User Name: CPSBACKUP$
Domain: CPS.LOCAL
Logon Type: 3
Logon Process: Kerberos
Authentication Package: Kerberos
Workstation Name: –
Status code: 0xC0000133
Substatus code: 0x0
Caller User Name: –
Caller Domain: –
Caller Logon ID: –
Caller Process ID: –
Transited Services: –
Source Network Address: 192.168.0.70
Source Port: 0
I log between 4 and 15 of these errors a day. the address is from a network file server. i’m running SBS 2003. anyone know how to fix this?