To hook up the Mac to the printer direct via USB cable you need to change the USB port type, do that via:
- Login to the printer as the System Administrator.
- Press the Machine Status button on the Control Panel.
- Select the Tools tab on the Touch Screen.
- Select Network Settings.
- Scroll down and select USB Settings.
- Select USB Connection Mode.
- Select Direct Printing using Driver.
- Select OK.
Now plug it into the Mac and it should see a printer, and at that point you would make sure you use the Xerox driver, because Apple will no doubt install it with their Generic Apple Print driver.
As for the error, that would imply you have something like Xerox Standard Accounting enabled, doesn't matter how the job gets there, you will get an error if you don't supply an XSA account (Not the system admin)
You have admin access though, so check if it is enabled and shut it off if it is.
Machine Status >Tools > Accounting Settings > Accounting Mode
The only other way to do anything that would cause such an error is to disable users from printing entirely, which certainly would have had to be enabled by someone on your LAN (It isn't available at the device and is never enabled by Xerox)
CWIS > Properties > Login/Permissions/Accounting > User Permissions > User Permission Roles > Edit
Edit
If none of that works, supply a picture of the fault
