It was reported some time ago that many Aperture users were seeing strange lines on their images after exporting to JPG. While it seemed that this problem was solved in v1.5.1 it seems that some people (including myself) are still having the problem from time to time.
The fix seems to be to download the Apple Digital Camera RAW Support Update 1.0.1 (Universal) which can be found HERE.
I downloaded the update, installed it and then did a test batch export and I did not see any nasty lines in my images. If you are having this issue, downloading the update seems like the thing to do.
Until next time,
Allen Rockwell Photography