Hello Léonie
Thanks for your reply. I was obviously too annoyed to be precies. This is what has happened:
1) Imported images form my CF card as referenced files (like the other 30'000+ images, copied to the HD when importing). All files residing on the main drive of my iMac (as all the others).
2) Made a an album with a subset of these images, then started working on the album, deleteing some images, applying adjustments.
3) Exported all images inc their versions as JPG. Worked will.
4) Then wanted to export all orignals of these images. It said that 0 out of 25 were exporeted. I then looked for the originals. They were all gone from the file system. Looked in the Trash - not there. Looked for the images with Spotlight - not on the hard drive.
Note that the previews are still acessible and only the files that I exported are gone. This is annoying. Not to mention that Aperture crashed in the meantime, then claimed the library is locked, I had to reboot and then to wait 30 mins for the library to be fixed as it was corrupted...
I am on Aperture since version 2 appeared - this is really a shame...