error code -38 was returned by the audio driver

I;m receiving the error message above. I'd been editing an audio file used in my Logic song with Soundtrack pro, but I made backups and besides, I'm not using the file any more! Now I can't hear my audio tracks any more.

I've tried repairing permissions...

Many thanks if anyone can help.
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Logic Pro 8.0.2
G5 2.3GHz, OS X.4.11