Powershell Script Scheduled Task Stopped Running (Could not Start)

I'm running a scheduled task (for Powershell Script) on Windows 2003 Server. I believe the script works fine. The task is scheduled to run every 10 minutes from 7:00am to 11:50pm everyday. However, it never gets to run more for than a day. It always stops some time in the afternoon (between 2pm and 6pm). I'm not sure exactly what happened but I always get the error

The attempt to log on to the account associated with the task failed, therefore, the task did not run.
The specific error is:
0x80070569: Logon failure: the user has not been granted the requested logon type at this   computer. Verify that the task's Run-as name and password are valid and try again. 

It seems like most people with this error are saying that they need to make user "logon as a batch job". However, this option is greyed-out for me. I search for other places where users have similar problems but the solutions are not written in detail (some of them have something to do with GPO). I've only used the basic features of Windows Server and I have no clue how to get to the place they are referring to.

Can someone please confirm whether "logon as a batch job" is indeed a solution and provide a detailed walkthrough on how to solve my problem?

Thanks,

That is indeed the issue. The reason you can't set this value could be related to Group Policy. Is the server in a domain? If so, please check group policy as described in the following article from Microsoft:

http://technet.microsoft.com/en-us/library/cc755659(v=ws.10)