Had the same problem last week, the client had changed the administrator password, also for things function properly you need to be logged in on the console.
To overcome the problem create another user account with administrator rights, name the account to something that identifies it with the process and use this account as the run as.
The client can change the admin password whenever the like without effecting the Scheduled process.

>can anyone identify a failure to execute an .exe from within the task scheduler with a return status of 0x80? At the same time I can't execute interactively from a shortcut either. This is a "sudden" condition affecting long-running jobs. TIA
>Howie