According to this:
http://www.coffer.com/mac_find/?string=00-15001560xxxxxx MAC address belongs to a Hewlett-Packard device.
Look for
- most likely a HP printserver [or network printer] - and reboot it, or
- less likely a HP workstation running NT/W2K/XP with IPX and having an own IPX number set.
You can also issue a TRACK ON on the server to see RIP/SAP communication screen
(use TRACK OFF to switch off, and RESET ROUTER to reset the internal router table and restart advertise/gather again)
[see RESET ROUTER section at
http://support.novell.com/techcenter/articles/ann20010801.html for more on this]