Creating scheduled task via gpo

I still have this problem and don't know how to solve it.

I have in windows 2008 AD - taks schedule over GPO for user to backup files from windows 7 client, to windows 2008 server.

Every user have mapped disk Z: which is actually some folder on server 2008.

Now in task schedule on server I made a job....

user which runs this job is NT AUTHORITY\System

run with highest privileges

runnnig program is batch file C:\Users\%username%\Desktop\copy.bat

and in batch file is this

robocopy C:\Users\%username%\Desktop z:\Users\%username%\Desktop /e /fft /w:1  /r:1 /ns /nc /nfl /ndl /np /copy:dt

I tryed everything and doesn't work, when I double click it on desktop it works, but over task schedule doesn't.

Can somebody helps me to work this out?

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I never left an open problem....I search, dig and ask, until it's solved....

lforbes