Importing midifile into Logic - No sound...?

I am trying to work with a midifile imported into Logic (Studio 8). Everything imports fine, the notes appear in the piano roll and the level indicators show signal on all the tracks but I can't hear any sound. I have checked that my other Logic projects play back OK and my audio devices in general all work as normal. I am using an Edirol FA-66 Firewire interface with the outputs of the midifile routed to outs 1 & 2 (which go directly to my studio monitors). Hoping someone can help me out here.