Exporting to quicktime problem/glitch

Wow, never seen that before. What format is the original? Did you optimize or use the original? Are there other background processes going on while you're exporting?

I'm assuming you're exporting with the Cmd-E option, right?

Here's what I'd try. First in the Project Library highlight the Project, in the File menu, delete the render files (don't do it on the Finder level, FCP X tracks render files in it's database).
Highlight any associated Events and delete their render files the same way.
Get the free "Preferecne Manager" app from Digital Rebellion (dot com) to properly, safely, and quickly delete FCP X's preference files.
Run Disk Utility to Repair all connected drives.

If those steps don't help, I'd maybe reinstall FCP X by move the app in the Applications folder to the Trash, launch Mac App Store, in the Purchased pane, click Install for FCP X. I'd also consider running Disk Warrior to repair the Directory on all attached drives as a final move.

But I bet it's bad render files and perhaps bad pref files. Try deleting those first. FCP X will build new ones from scratch next time it's launched.
 
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