Export Podcast Fails

I’m using Garage Band version 4.0, build 221, on a Dual Core Intel.

I have a recording of a class I taught, about an hour and 50 minutes long. Every time I try to export it, the export fails. Far as I can tell, no file is even created although GarageBand for some time displays a window purporting to show progress.

Any ideas?

-Lofty