Yeah, 'open iTunes' doesn't work.
What I do is open last.fm FIRST, iTunes can't already be open. Then open iTunes, and close out last.fm (it'll remain open in the background) and everything scrobbles.
But for some reason everyday it stops working I guess 'cause I close my laptop, so before I start listening each day I have to open the Task Manager and end iTunes + last.fm, and re-open them.
If you go to your profile while listening to music and it's not showing 'listening now', it's not working.