似乎有密码问题，已在以下帖子中解决:

It seems there is issue of password which is resolved in below post :

https://social.technet.microsoft.com/forums/windowsserver/en-US/fe7345ea-b037-469b-b425-17d5fee28e91/windows-server-backup-wont-schedule

SYMPTOMS

When you try to change the run as user for a scheduled task in Server 2008, The task is currently configured to runas SYSTEM. Using the following command line he receives the error. 

c:\>SCHTASKS /CHANGE /TN TestTask /RU TestUser 

SCHTASKS prompts the user for a password for the runas user account. After entering the password it displays the following error. 


"ERROR: The task XML contains a value which is incorrectly formatted or out of range. (52,4):Task:" 


The task's runas credentials have not changed. 


RESOLUTION

To avoid this error you must add the /RP option with an "*". The new command line will look like this: 

c:\>SCHTASKS /CHANGE /TN TestTask /RU TestUser /RP * 

SCHTASKS prompts the user for a password for the runas user account. After entering the password the task is updated without error.