Thanks leonieDF
Fixed!
I had already tried to rebuild the library, but i could only do it through aperture 2, cause as soon as i opened Aperture 3, it started rebuilding the library, and deleted everything. The files might have been somewhere temporary, cause there wasn't space for copying a new version of the 260gb library back to the internal harddisk, even though the finder showed 340 gb free space. Tried grand perspective (app that shows you a graphic version of your harddisk) and it didn't show it either.
Third time i didn't rebuild every image, but only imported the files. Guess they have to be rebuild if you want to use every tool on top.