"Playback" plugin not playing AIFF file

I've loaded an AIFF file that works in the actual "Playback" plugin (e.g. when I hit the Play button on the plugin itself). But frustratingly, it will not play in the main Perform section. The little wave form window does not advance; no sound comes up; nothing. I am at my wit's end, as there doesn't seem to be any reason why this should be happening. Please help, thanks!