hi ecrocker,
Without knowing more about your set up, I'll just give you some general things to check or do.
One is to make sure that the new upgrade you have installed is from
www.winmxgroup.com If your not sure where you got the installer or it doesnt say Patch Operational in the update bar, its worth redownloading and installing from that protected patched version.
Second make sure your firewalls are actually allowing MX to connect ok. Often when you upgrade from an older version some firewalls, including the XP ones see this as a program hijack and block it even though previously you've allowed it. Remove WinMX from any firewall rules you have allowing it, restart the program, and allow it again when the firewall asks. Or manually go in and add it after restart.
If you had ever set up a router or DSL modem before with certain port numbers, be sure those are set in the New WinMX. For example if you used port 1720 and 2343 in the past, the new WinMX may have them set back to defaults in Settings > Incoming TCP 6699 and In/Out UDP set to 6257. Just make sure all ports match in router, modem, firewall and WinMX.