LW unable to connect. (Tried everything)

I've tried everything that's been suggested in the hundreds of pages on this forum, dealing with LW connection issues. Nothing has worked.

I *think* I know the reason for the connection problem, but I've no idea how to solve it

I use 2 systems:

Here's my system configuration of System 1:
With this configuration, Limewire works perfectly!!

Now here's my system configuration of System 2:
With this configuration, Limewire fails to connect.

Here's what I've tried (unsuccessfully) so far:

1. Uninstalled (completely) and reinstalled Limewire 5.0.11
2. Uninstalled (completely) and installed Limewire 4.18
3. Deleted the preferences file/folder
4. Added Limewire as an exception in the Windows Firewall
5. Added Limewire ports as exceptions in the Windows Firewall
6. Turned off Vista's Firewall
7. Disabled Vista's Firewall completely (even from starting up on reboot)
8. Turned off Windows Defender completely
9. Disabled Windows Defender completely (even from starting up on reboot)
10. Added Limewire as an exception with full "Allow" permissions in NIS 2009's Smart Firewall
11. Turned off NIS 2009's Smart Firewall
12. Turned off everything (Windows Firewall, Defender and NIS' Smart Firewall)
13. Changed Limewire's listening ports to a variety of different numbers
14. Changed Limewire's connection from uPnP to Manual Port Forwarding
15. Changed all the "Performance" options in Limewire

As a last resort, I completely disabled Norton Internet Security 2009 from starting up (from the System Configuration tool, msconfig). I disabled all of NIS' services and startup programs, in addition to having turned off my Windows Firewall and Defender (see steps 06 and 08 above).

Viola! Limewire was able to connect.

On the problematic machine, I tried using "MP3 Rocket", and it worked!! However, NIS 2009 has suddenly decided that MP3 Rocket is a virus and keeps deleting it and refuses to let me download it.

Some obvions conclusions seem to jump out:
a. Obviously turning off NIS 2009 is not a solution.
b. Obviously my router's firewall is not causing the problem.
c. Obviously the problem is because something within NIS 2009 is blocking Limewire.

My questions are:
1. Does anyone have any idea on what in NIS 2009 is blocking Limewire?
2. How do I get Limewire to work, while keeping my machine reasonable secure?

Some folks are going to suggest that I use a different AV provider. Please note that this is not an option. For financial and political reasons, I'm stuck with NIS 2009.

Thanks in advance!