Why won't Aperture exported jpgs open in Lion?

A while ago I exported my most important projects from Aperture 1.5.6 into a folder that subsequently would contain folders for each project. Names of the exported jpgs within each such folder, are in the format "2005-02-03 19-46-29.jpg". They all differ in file size and opening them in BBEdit shows that they are not all zeros. All in all, there is about 14GB of jpgs that were exported this way. None of the jpgs will now open and I am at a loss as how to repair all of these files. The error that Graphic Converter returns is: "-003:'Forbidden' prefix found in file 2005-02-03 19-46-29.jpg ..."

Here are my current system specs:

iMac 2009, 2,8GHz core i7, 12GB RAM, running 10.7.5 (11G63)

The files now reside on an external FW disk.

What I have already tried (with no luck) is:

- repair permissions

- opening in Photoshop

- stripping EXIF (and other) metadata from jpgs using Graphic Converter 6.7

- changing file names and extensions

- trying to open them on another system

- trying to import into Aperture 3

- checked disk health with Disk Utility (all disks are ok)

Any help would be greatly appreciated.

Best regards,

Tobias

Stockholm