Exports will not Cancel

You might check, if you have an incompatible image export plug-in installed -

To use a plug-in with the latest Aperture release, it needs to be sand-boxed and 64-bit compatible. Try to upgrade your plug-ins to compatible versions, if possible, see:

Aperture 3.4 and later: Some third-party plug-ins are no longer compatible

Also you might try to remove your image export presets and other presets used on export from your user library (after quitting Aperture)

~/Library/Application Support/Aperture/Export Presets.plist

~/Library/Application Support/Aperture/Raw Decode Presets.plist

What is your Aperture version, and Mt. Lion version? Did you install Aperture 3.4 or 3.4.1? The Aperture 3.4 installer had a bug, and if you used that installer, it might be adivisable to reinstall Aperture, if the above measures do not fix the issue:

See: Aperture 3.4: May quit unexpectedly on launch after updating

Regards

Léonie

That is typically the case, when one image in the Library is corrupted and Aperture cannot render the version from the master image file.

If a single image is the culprit, you should be able to export a test image. Import an image for testing, that you have checked in Preview. Try to export that singel image. Does it work?

If you can export new images, try to find the corrupted image or video.

Launch Aperture with the Shift-key held down to prevent it from trying to render previews and stalling. Then try to manually render previews for small groups of images from your most recent import.

To manually render previews select the images in the browser and use the command "Photos > Update Preview/Generate Preview" from the main menu bar.

Aperture will stall again, when your current selection contains a currupted image original or version.

Léonie

Found the problem image & deleted it -

What kind of image? Raw, jpeg?

Can it be that you have more than one corrupted image?