Ever since the new update for LastFM, I've been having problems with scrobbling. Everytime I turn my computer on and try to listen to music through Winamp and have to re-install the plug-in or something. So yeah what the hell am I supposed to do?
I checked the last.fm forums real quick and it sounds like someone is having a similar problem to you. The software keeps failing since the update. I'd suggest posting there and asking for help if you don't get a fix here.
I'm having a problem with winamp now. When I play a song it's like going fast forward.