I recently had this problem with WWW::Mechanize, which I understand to be derived from LWP::UserAgent (one of the other posters mentioned LWP...)
For me, it always works in the browser and failes in LWP...
Not even sure if this is even remotely helpful, but maybe it will spark an idea...Here is what the packet trace said:(I will be posting to a perl newsgroup later, so if I get an answer I'll post it back here)
src: tcp connect, flag = sync
dst: flag = ack, flag = reset
src: flag = sync
dst: flag = ack, flag = reset
src: flag = sync
dst: flag = ack, flag = reset
<THAT'S IT>