I was getting this error message on my SBS 2008 Server:

Log: Security
Type: Failure Audit
Event: 4625
Agent Time: 11:26:36 am 4-Apr-09
Event Time: 3:26:36 pm 4-Apr-09 UTC
Source: Microsoft Windows security auditing.
Category: Logon
Username: N/A
Computer: ICS-S01.ics.local
Description: An account failed to log on.
Subject:
 Security ID: S-1-5-18
 Account Name: ICS-S01$
 Account Domain: ICS
 Logon ID: 0x3e7
Logon Type: 3
Account For Which Logon Failed:
 Security ID: S-1-0-0
 Account Name: ICS-S01$
 Account Domain:
Failure Information:
 Failure Reason: Unknown user name or bad password.
 Status: 0xc000006d
 Sub Status: 0xc0000064
Process Information:
 Caller Process ID:  0xc88
 Caller Process Name: C:\Program Files\Microsoft\Exchange Server\Bin\Microsoft.Exchange.Search.ExSearch.exe
Network Information:
 Workstation Name: ICS-S01
 Source Network Address: -
 Source Port:  -
Detailed Authentication Information:
 Logon Process: Advapi
 Authentication Package: Negotiate
 Transited Services: -
 Package Name (NTLM only): -
 Key Length: 0
This event is generated when a logon request fails. It is generated on the computer where access was attempted.
The Subject fields indicate the account on the local system which requested the logon. This is most commonly a service such as the Server service, or a local process such as Winlogon.exe or Services.exe.
The Logon Type field indicates the kind of logon that was requested. The most common types are 2 (interactive) and 3 (network).
The Process Information fields indicate which account and process on the system requested the logon.
The Network Information fields indicate where a remote logon request originated. Workstation name is not always available and may be left blank in some cases.
The authentication information fields provide detailed information about this specific logon request.
 - Transited services indicate which intermediate services have participated in this logon request.
 - Package name indicates which sub-protocol was used among the NTLM protocols.
 - Key length indicates the length of the generated session key. This will be 0 if no session key was requested.