wlm keeps losing webcam connection

I'm trying to use wlm with a 3com HomeConnect usb webcam on winXP SP2. Problem is, messenger keeps 'losing' the webcam. I have a
second AV camera connected to a Videomate TV card in my PC. If I go through the audio and video setup wizard first time I can
select the usb webcam and see the image. If I then click on tools/webcam settings I see the webcam image again. But when I click
Close and then tools/webcam image again this time I get the videomate camera image. It's as if clicking Close switches off the
webcam and it won't come back again. And if I go through the audio and video setup wizard a second time I get a grey box where
there should be an image and a message saying 'cannot connect to the webcam'.
I've got the latest driver installed for my webcam. Is there a solution to this? Thanks for any advice.