Timeline Thumbnails
Sometimes clips appear in the Timeline without their thumbnails as if the clips were offline. This is most likely to happen when material is reconnected and the poster frame at the beginning of the clip doesn't update.
Though annoying this really isn't a significant problem. The solution is usually simply to force the application to update the thumbnails.
Quit the application and go to your Thumbnail Cache Files folder. This folder's location is specified in the Scratch Disk panel of System Settings.
Open the folder and delete its contents usually the Final Cut Pro or Final Cut Express Thumbnail Cache and Thumbnail Data.
Relaunch the application and it will automatically rebuilding the missing thumbnails files, using the first frame of the clips in the Timeline.
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