1.5 is that the LW version? A version that old will not only give you problems but may be blocked by many a person you attempt to connect to. Many of the protocols of design & use on the network community have changed since then which is why LW does not normally allow the older versions be available. This goes for almost all the Gnutella network programs. Some have in-built filters that will stop older versions connecting to them.

I'd have recommended uninstalling Java 1.5 & trying Java 1.4.2 instead. Sometimes Java 1.5 doesn't behave well on some people's systems. There's also a chance your 1.5 was corrupted due to being installed over the net. That's why installing from your comp is wiser.