I've had several problems connecting my laptop to my 561 processor. Predictability of connection was poor, but on my last play with the 561, I found that quitting the following programs on the laptop did the trick:

Norton Antivirus
Norton Cleansweep/Smartsweep
Norton Internet security
Psion Psiwin

I'm not sure whether one or all played a part in the connection problems, but if all were disabled prior to reopening the Meridian software, I could get a link. And consistently at that!

I believe Windows XP has a built in firewall, so if that can be disabled, along with any antivirus software, it may do the trick.

Best of luck!