Previews not being generated

When I first set Aperture up during the trial, I left all the in the iPhoto library and referenced them. Since then I bought Aperture and now have it managing almost all of my masters (JPEG only at present).

Like some others on the forum, I noticed that I was having problems with images showing up in the 'Aperture library' in iWork/iLife. It seems that only the imported example projects (with previews already) are showing up.

I originally just entered the Serial Number into the Trial version but have since tried:
0) Rebuilding the library via Command-Option on launch
1) Updating Previews at various times both for the whole Library and for individual projects. If I delete all previews first then I can't even see the example projects in iLife/iWork.
2) Reinstalling from 1.5.1 on DVD and using Software Update
3) Removing Aperture, deleting all the receipts and reinstalling again
4) Repairing permissions
5) Deleting the library and recreating it from a Vault
6) Adjusting the preview size and quality and currently have it at 1280x1280 at 6
7) Importing the library as a different user: lots of time 'generating previews' but no more success.

During this process, I decided to investigate properly inside my Aperture library and noticed that it does not seem to generate previews at all for me (despite 'Processing previews' in the 'Task list' window). ApertureData.xml seems to only contain ImagePath entries for the example projects (unless I deleted their previews during the troubleshooting process)

At one stage I wondered whether it was connected with my camera as pictures from my (and other people's) Canon A95 seem to need to be imported via iPhoto before Aperture will read them properly. However, photos from a different (JPEG) camera do not form previews and nor do the IR RAW files mentioned recently on this forum (and generating all new previews from the example projects does not work).

Except for the previews (and the Fullscreen filmstrip window popping up over other windows when in workspace layout, but that's another issue) my experience so far with Aperture has been very positive.

Can anyone suggest anything else to try? TIA.

I notice that every time I start Aperture it claims to be processing all my previews. If I try a slideshow, it seems to get stuck 'Rendering Previews' as the progress bar does not advance (including an example project with previews deleted). Of course, the slideshow works for the example projects with their original previews intact.