Have you recently imported videos? Maybe Aperture is hanging while trying to process previews for the video clips. I'd try to launch Aperture with the shift-key held down to defer the generation of previews. If you can launch Aperture this way you can inspect your last import and see, if there is anything peculiar with one of the last imported items.
Interesting, that does seem to make the problem "go away" for that run. After quitting and relaunching though, the problem is back.
So it's definitely related to the thumbnail generation of videos. While in Aperture, I tried to watch a video and had no problems.
I wouldn't say there's anything "peculiar" going on - I just import photos and videos from a folder where they've been downloaded by Eye-Fi from my camera. The items are sometimes in the Aperture library itself (when I'm not connected to the Time Capsule), but I periodically go and "Consolidate Library" which puts all the actual files on the Time Capsule.
As a work-around, you could quarantine your videos in some dedicated projects and disable the preview generation for these projects permanently. The option to enable/disable preview generation for a selected project is in the drop-down menu behind the cogwheel at the upper right corner of the Library Inspector panel.
but I periodically go and "Consolidate Library" which puts all the actual files on the Time Capsule.
Do you mean "Relocate Originals"? Or is your Aperture Library actually on the Time Capsule?
Even if that would help (and thanks for getting me this far), I'd rather not permanently disable video previews. I've been using iPhoto instead of Aperture while this gets fixed, and Yet despite waiting the last upgrades of Aperture and Mac OS X neither have fixed the bug.
Perhaps there is some way of forcing some kind of a reload of video, or of changing permissions for those actual files?
The menu command as it turns out is "Relocate Original" which lets me "move" all files into the Aperture library's Storage in the file system. Because my Library is not a "Managed" library, the library file itself is on my Mac, while the photo/video files are all on the Time Capsule.
Because my Library is not a "Managed" library, the library file itself is on my Mac, while the photo/video files are all on the Time Capsule.
This may be a network problem. Have you tried, if Aperture still has problems, if you consolidate some of your videos ? I'd pick a few of the videos, consolidate them into the Aperture library, then export a new test library with only these videos. And then check, if you still see the qtkits error, when the video is managed.