Unable to get audio Input from FastTrack

Hi There,

For a wee while I've been using and Avid Fastback solo as a USB interface to plumb my guitar into my mac.

I bought MainStage 2 a while ago and, frankly, found it a bit baffling. But I decided to tackle the beast and strapped myself in...

Unfortunately, although the programme recognises my audio interface, when I select it I get no audio, nada, zilch.

Now, checking in system prefs, the audio interface works fine, I can use it perfectly with Garageband but no dice with MainStage.

I've even updated to MainStage 3 but it's not helped.

Does anyone have any idea what might be going on ?

Thanks

Richard