[linux-audio-user] Audacity error

(de-lurk mode) Hi all, I keep getting an error when starting Audacity. It reads "There was an error initialising the audio i/o layer. You will not be able to play audio". It then starts & works, apart from not being able to play what it is doing. The strange thing is that it worked fine the first time I used it (I recently "rested" Debian in order to try Ubuntu, so it's a new installation). Every time since then, it has shown this error. Everything else seems to be working fine on the audio front: XMMS is happy, MIDI is working, even Audacity is functioning, but I have to play files saved in Audacity via XMMS. Is there something silly that I've missed? I can't work out why it would play audio once & then not subsequently. Any help appreciated. TIA Gavin.