Why don't you dump BT. Although I'm on AOL bb here at work, I use Tiscali PAYG at home. Admittedly I only use it the occasional evening and at weekends, but it's only 1p a minute. Although many may say they don't like them, personally never had any problems.
Tricky one that. This is where you'll realise that I have no idea what I'm talking about, but it almost sounds as though it's something to do with the fact that there IS activity, and it can't handle it. Have you asked BT, or can you uninstall and reinstall? Not much help am I. :o(