I could reformat, but I wonder why Finder has no issue, but Aperture does?
I did drag the images in to overcome this, which is not a big deal, but it is nice and easy when it does work in Aperture without having to navigate into the card to find the pictures. Why do you prefer to do it that way anyhow?
I have got the same trouble.
Sometimes it works fine: Aperture recognises my sd card in 10 seconds after I inserted it.
But usualy it takes 2 minutes or more.
Sometimes it can help, if you unmount and insert the sd card again.
The simpliest way is to drag images into Aperture, but if you want to import only a part of images from the sd card, or you have already imported some of images and don't want import all images again, you lose
And, if I import images of many different days into different projects, Aperture can not delete all of imported images at the end.
IMO it is a very bad idea to let Aperture or any other images management app have direct access to one's not-yet-backed-up originals. Sometimes there are just "anomalies" such as you are experiencing, but worse things can happen.
Suggested workflow steps:
• Use a FW card reader or MBP slot to copy to a file folder on the SSD or hard drive. With fast camera cards copy times are quick, but cheap slow cards can slow this step down a lot.
• Eject and physically disconnect the card reader.
• Back up that file folder on external drive(s).
• Only after backup is complete and verified, reformat the camera card in-camera.
• Import images into Aperture from the file folder on the SSD or hard drive.