Hello,
Maybe it's not too late for some of you :-)
In case you have multiple network connections on your computer (physical connections, vpn, etc.) there is solution for "Device not found" or offline device in Network Scan Manager. The solution is changing the prority of your network adapters and put in top of the list your network adapter directly connected to the Xerox device. I don't know if there is such an option in Windows XP, but in Windows 7 exists and solves this annoying problem:
http://support.microsoft.com/kb/2526067
Best regards,
Catalin Bucur.