How did you create your smart album? Has it been imported from an old iPhoto LIbrary?
Then I'd try to open the Aperture library in iPhoto, if you are using Aperture 3.4.3 and iPhoto 9.4.2.
If it is not a smart album from iPhoto, I'd try to repair or rebuild your Aperture library, see:
But one more question: Do you know, which images or videos the smart album contains?
- If you try to browse the images in a different way, by accessing them from their project, does Aperture crash as well?
- Does Aperture crash if you recreate the smart album with exactly the same smart settings?
What are the rules you used for the album?
Markus, there is a bug in Aperture 3.3 and later:
If you sort your projects by date and have smart albums, that have been imported from iPhoto, this can crash Aperture, see: Aperture 3.3.2 unresponsive if library contains old iPhoto albums - solution
What is exactly your Aperture and iPhoto version?
Since you even cannot select the smart album in iPhoto, check the setting of the "Keep projects and albums arranged by" option: (from the cogwheel in the library inspector panel)
Set it to "Manual", if it is set to "Date".
Now try, if you can delete the smart albums.