I have the same "brick wall" problem with both DSL and Cable (also same U10C018.80 cable modem) and switching from a much older free version of LimeWire to LimeWire PRO didn't correct this problem. My MAC G4 OSX 10.4.11 system firewall and my NETGEAR WGR614v7 SPI firewall are both turned off and I have no other firewall software installed. I haven't yet tried a complete deinstall/reinstall of LimeWire yet and I haven't Googled anywhere that says there's a firewall in the Cable modem. Did you ever solve this problem?