Black crop on exported images

Hello!

I've been using Aperture for some years now and I'm used to it and like it.

After switching to El Capitan I tested it and actually it still seems to work... BUT : as soon as I edit an image (that's what I bought Aperture for) it turns out with a black crop on the right hand side of the picture after export. The image looks ok in Aperture but the black crop appears after export. This is VERY frustraiting as I am not able to use my edited images...

I tried to search in the export options without finding any solution.

Any hints or help?

Thanks a million if anybody can help me!

Best,

David