Problem with new primary, same secondary machine

Hello! I have been using Multiplicity Professional since switching to Vista and discovering that Maxivista no longer works (such irony!). Multiplicity worked like a charm immediately after installation! I have a Vista laptop as primary and an XP desktop as secondary. Enter the problem: I had to send the Vista laptop back, and now I have a new Vista laptop. I installed MP on it, and it wouldn't find the secondary computer. I copied the .sig file from the old laptop to the new laptop's installation folder. No effect. I changed the workgroups to match (a strange requirement) on the two computers and now my Vista laptop can find the secondary (XP) system, but it can't establish the Multiplicity connection. It gives me the standard message about not being able to establish communication and checking firewalls and ports. I have NIS firewall and Windows firewall turned off on Vista. I have Zone Alarm and Windows firewalls turned off on the XP system. I have no idea how to open that 5-digit port number on either machine, but I don't believe I had to do that with the old Vista laptop. I've searched everywhere in this forum and have found no answers.

HELP!!

Thanks!
Don
p.s. I can't restart the XP machine because there's a long-running job on it that will need to run for a couple more days. Otherwise I'd try that, but then again this is the same XP machine that worked like a charm as the secondary machine for the original Vista primary.