Missing master files / Version-0.apversion

Greetings,

i have an inexplicable error in Aperture 3. I have migrated my photo library into aperture and allowed it to "ingest" the photos. Prior to this, i was using the browser/finder as the interface of choice for managing my files.

Now aperture is creating this error for a small number of files. When in the browser, the thumbnail is replaced by a dotted white outline bearing the filename Version-0.apversion or Master.apmaster.

When i double click on the thump, the screen will flash between the image and the grey background. In the meantime the Processing indicator at the bottom of the screen will fire up and the Activity monitor will display a never ending "Updating library" processing task with the counter going into the thousands. All 4 cores will fire up at the same time, but only when the app is in the foreground, when aperture is minimized, then the processor activity will stop.

I have tried to export versions or the originals, nothing happens. A directory with a Version-0.apversion or Master.apmaster file (4k) will be created.

I dont know how to address this issue and i have not been able to find anything online. I am looking forward to any ideas.