Security Event log error message for audit failures

Hello,
We have a small problem with SQL 2005 on Windows 2003 SP1 - well not exactly
a problem because all is working fine.
We have our security event log filling up with audit failure messages from
time to time.

Mydomain\ktest is my login with which I logins.
Mydomain\sqlserviceaccount is login used to start SQL services.
NT AUTHORITY\SYSTEM is already added as 'sysadmin' in SQL 2005.
Server8740 is the server in queston.

The messages are as follows:

Privileged Service Called:
Server: Security
Service: -
Primary User Name: ktest
Primary Domain: Mydomain
Primary Logon ID: (0x0,0x1330122D)
Client User Name: -
Client Domain: -
Client Logon ID: -
Privileges: SeTcbPrivilege

and

Logon Failure:
Reason: Account currently disabled
User Name:
Domain:
Logon Type: 3
Logon Process: Authz
Authentication Package: Kerberos
Workstation Name: Server8740
Caller User Name: sqlserviceaccount
Caller Domain: Mydomain
Caller Logon ID: (0x0,0x1302E)
Caller Process ID: 1164
Transited Services: -
Source Network Address: -
Source Port: -

I've already checked all permissions under local security policies and given
gave SQL service account Admin rights on Windows level, but still the same
problem.

Can someone shine some light on this?

Thanks.
Kunal.