Thanks for the reply DarthBilly but I'm no further forward :(
I logged on to the machine as the Domain Admistrator and owner of the accounts (I wasn't before). This is one of the accounts where BE doesn't accept the current AD password.
In Logon Account Management I select the System Logon Account, click 'Replace', select the account (which is a Domain Admin) that I want to be the new SLA and get the error - 'Unable to replace old Logon Account with new. The server has received incorrect or invalid data.'
I try and delete a non-Sytem Logon Account and it says it cannot be deleted because the following users have selected it as their default logon account and one or more are currently logged on to the media server. This user account is not logged in on the Windows box and no services or jobs are running under this user account.
I have already got the different jobs running under a different account but I'm having random failures. Testing the credentials within the job's properties passes and there definitely is no reference to the accounts I'm looking to delete in the GUI.
The situation I'm facing is that I do not make any changes to credentials or configuration and randomly get errors with the failure message 'The logon account that was provided does not have valid credentials.Ensure that the user name and password are correct, and then try again.' but the next time the job will be successful with exactly the same configuration. I would expect this error to be permanent.
Without any proper evidence I am suspecting that the jobs are somehow reverting back to the Sytem Logon Account if there is any delay with the specified account credentials being returned as successful.
I do know that this BE installation was installed as an upgrade to a previous version of BE (I don't know which version) but I've already resolved issues with automated catalog jobs running that aren't supported with this version and issues with the catalogs being merged into its SQL database. I've also recreated the jons to no avail.
So, I'm left with Logon Accounts in BE with faulty credentials and would like a way of cleaning them up to see if it helps.