Unable to import my iPhoto library to Aperture.

What Mac are you using and how much memory do you have? I was able to import an iPhoto library of about 15K images in one shot without issue. I would try the following if you have not already done so: 1) repair or rebuild the Aperture Library to remove the existing corruption, or create a new library, 1) repair permissions, 2) repair disk-using Apple Disk Utility (you will need to start up from another disk, 3) recognize you may have one or more images in iPhoto that are corrupted--try importing a few images and then gradually build up to 5K to 10K images (or less) at a time into Aperture to isolate the problem. You should also consider turning off face detection initially.

Would you consider doing an Import From iPhoto in which you leave the masters in iPhoto?

As suggested, you may also have corrupt images in the iPhoto database. If you have Aperture’s Activity Window open, did it give you any indication where the problem was occurring.

I understand you may be getting frustrated, but your description of the problem has me wondering what you are seeing. You can try to repair any problem and redo the import (first select the option: “do not import duplicates”).

"Photos unusable" may be describing the weird image Aperture displays when it cannot find the master. If your Aperture Library is functional, you can use the iPhoto Browser within Aperture to import individual photos that had a problem. But I’m not sure if you are at the stage where you have already generated Previews and if it’s just the Previews that are weird and need to be regenerated, or the Thumbnails that need to be redone. If only the Thumbnails are bad, post back for further instructions to save correct them.

Be sure and disable Faces and Places in Preferences while you are initially building up your Aperture Library; you can turn them on later if you wish.