Aha! I was just fooling around with Net::AIM trying to get it to do what you want (I was able to send the message by using a handler called when first logged on, but I can't exit without screwing up the handler.) and I think I figured out at least part of your problem.

It seems that AOL will block users who connect and disconnect frequently. I ran into this problem when suddenly it wasn't sending messages anymore. I tried to log on using GAIM (a very nice AIM client for Linux) and got the message about connecting and disconnecting too much. If you've been testing with the same username, you might want to try and register a different to test with; either that or wait for a good amount of time before trying again.