No idea, maybe you are behind a firewall after all and your school is blocking access to the LimeWire hostscache router.limewire.com.

In that case, connecting won't be quite as easy. However you might want to try connecting to router2.limewire.com:6346 or router3.limewire.com:6346. Maybe one of them works.

If your school blocked access to the destination port 6346 completely to prevent its pupils from downloading cheap pr0n, you won't be able to connect at all.