If you have removed a required right, you will receive the subject error.
The rights needed to run Sysprep are:
Back up files and directories
Modify firmware environment values
Restore files and directories
Shutdown the system
To resolve this problem, use the Local Security Settings or, if you removed the rights in a Domain, Site, or Organizational Unit, modify the Group Policy for the domain:
1. Expand Local Policies and double-click User Rights Assignment.
2. If you need to add a right, double-click the right and press Add.
3. In Select Users or Groups, select Administrator and press Add.
4. Press OK and OK.