Problem:
Event Type: Warning
Event Source: SQLAgent$SBSMONITORING
Event Category: Job Engine
Event ID: 208
Date: 13/04/2010
Time: 3:00:00 AM
User: N/A
Computer: APF-MA-DC01
Description:
SQL Server Scheduled Job ‘SBS_Database_Cleanup’ (0xCFE15C1485482B4AB05D5AA0CE0721D1) – Status: Failed – Invoked on: 2010-04-13 03:00:00 – Message: The job failed. Unable to determine if the owner (MYDOMAIN\oldaccount) of job SBS_Database_Cleanup has server access (reason: Could not obtain information about Windows NT group/user ‘MYDOMAIN\oldaccount’. [SQLSTATE 42000] (Error 8198)).

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.
Fix:

Login to the correct instance of SQL using osql.exe (try -U sa and a password or -E to authenticate as your currently logged in account)
osql -E -S SBSSERVER\SBSMonitoring

USE [msdb]
GO
EXEC msdb.dbo.sp_update_job @job_name=N'SBS_Database_Cleanup',
@owner_login_name=N'DOMAIN\ThenewOwner'
GO

Cause:
This was caused due to me renaming an admin account. When the SQL Agent ran the job it couldn’t find the account in AD and so failed to run it.