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I know this is a really old question, but has your issue been solved?

I had the same problem where I would export and at 100% it would hang forever until I hit cancel. I was running FCE 3 and running on Snow Leopard.

I read on another forum (see link below) that if you are using an older version of Final Cut Express (v3 or less) and are running Snow Leopard, FCE might not work properly. I upgraded to FCE 4 and instantly it works and I am able to export successfully!

Hope this helps.

Link - http://discussions.info.apple.com/thread.jspa?threadID=2430494&tstart=0&messageID=11525669
 
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