WHich ISP is it?
There had been a recent inrush of users from
Insight which is a
Limewire blocker
Comcast is another that apparently has been guilty in the past. And Cox & EURO1NET & TISCALI are also in this. Of course Cox doesn't seem to apply to all users but just selected one.
If it's not your isp then there might be something wrong with your configuration to allow LW access.