Actually, 00-00-00-60-13-BB isn't a UUID, it's a network adapter MAC address, and it's not really a valid one of those either. UUIDs are 16 bytes long, and that length means that generating a "random" number pretty much suffices for it to be a unique ID. MAC addresses are assigned to IEEE 802 network adapters, and have two parts; the first three bytes are assigned to specific manufacturing organizations (you can look up the ID assignements at
http://standards.ieee.org/regauth/oui/index.shtml). The 00-00-00 OUI prefix was assigned to Xerox - where Ethernet was first designed - for instance.
With 7.5, it is the MAC address of the network adapters that is used by the server to identify clients; using the SMBIOS UUID of a system was not supported until GSS2. SImilarly, the ngserver.log file is new in GSS2 (there's a procedure for bringing up a similar diagnostic display, which I'm managed to forget - holding down the Control key and moving the mouse to the top-left corner of the dispay, or something like that - it works on the clients and the server to bring up a tray icon which has opening a debug window as an option).
With a 7.5 client, the reasons for not showing up are slightly different; if the client thinks it's in contact and isn't showing up, it's probably a similar kind of problem to the one discussed in this thread, but the details are different. Some software network adapters claimi to have valid-looking MAC address assignments, and these can cause the clients to be misidentified (the Microsoft loopback adapter is one such - we've tried to filter out the more common problematic IDs, but that one managed to slip through).
If the client thinks it isn't connected, then it's generally a matter of exploring the network.