My Robocopy backup script has a few lines of:
robocopy D:\Source_Dir K:\Backup_Dir /MIR /B
This worked fine on Windows XP, but stopped working once I moved to Windows 7. Robocopy would give the following error:
ERROR : You do not have the Backup and Restore Files user rights. ***** You need these to perform Backup copies (/B or /ZB).
Surprisingly, I would get this error even if I was logged onto an Administrator account!
The reason turned out to be that running in /B (Backup mode) requires permissions to open files without any security restrictions. With the UAC in Windows 7, even a normal invocation of cmd.exe by an Administrator account does not have these rights!
To run Robocopy in /B (Backup mode) one needs to start cmd explicitly with Administrator rights! To do this type cmd at the Start menu, right-click on cmd.exe and choose Run as Administrator. This works fine even from a non-Administrator account (assuming you know some Administrator credentials.)

but what shoud i do if i have a relative path as source? .\
if i run it as admin windows sets the relative path to c:\windows\system32\
Andreas: Use the absolute path
Andreas: or add a line to your batch file that changes to the batch file’s directory first: cd /d %~dp0
Am running this command via Robocopy GUI 3.1. How can I solve this error?
Donald: I have not used RoboCopy GUI. But, you could try running this app in Administrator mode.
Fantastic. It worked for me. Thank you so much