Don't run the XP firewall & McAfee together. Choose one, configure it to allow LW & disable the other firewall.After up_dating or upgrading it's a good idea to delete LW's preferences folder when LW's properly closed. See point 3 here & also point 2 if you've used older versions of LW in the past (there could be a folder in either location).
Fixes for LimeWire
This will kill all of your settings within options, you'll have to go back through afterwards & reset things.

Have you updated your Java version since buying Pro? If so, you could always try this earlier version of Java (some people have had problems with 1.6.0_01). Use the JRE offline installer & remove your current Java version before you install this one.
Java SE Downloads - Previous Release - JDK 5

Your modem has a firewall. How did you have it configured with the earlier version of LW (UPnP enabled, port forwarded or neither)?
You could try port forwarding. The instructions are here.
Port Forwarding for the Siemens Speedstream-6520
Don't forget the step of setting up a static IP address. LW's listening port, port in the 'manual port forward' box & port forwarded within a router/modem must all be the same number.

I don't know how you managed to get a 4.13 Beta after downloading 4.12.11...since you would've downloaded from your personal download page, which gives you the choice of downloading either the stable release or the Beta