Did this happen directly after upgrading to Aperture 3.4.3?
The problem with the Aperture 3.4 update is, that in some cases it did not install the correct "Account Configuration" plug-in, and so the FaceBook publisher plug-in will not work. This is supposed to be fixed by installing the update 3.4.1 update, but if you directly upgraded to 3.4.3 you might have missed the bug fix with the 3.4.1 update. When you look at your crash log - does the crashed thread contain calls to the "FacebookPublisher"? Then it probably will help to reinstall Aperture from the original media, as described in this support article: