Sooner or later it happens to almost all digital photographers - at least all those who shoot a lot. You check some of the images in camera and they look good. You load the memory card into the reader and wait for the images to appear in Aperture’s import window. But nothing happens. You push the card into the reader a little more firmly and make sure the reader is attached properly to the computer, but still there’s no sign of the card showing up on the computer.

The first time it happens it’s hard not to panic, especially if the card contains shots that will be difficult to replicate. Plus you wonder if the card is corrupt and should be replaced, or if you can salvage it. And you wonder if it just happened out of the blue or if you somehow contributed to the failure.

Memory card recovery software applications such as Photorescue (www.datarescue.com) and similar programs can frequently recover the images from your card even when the card is not visible as a drive in the Finder window. Often the problem is that the directory on the card has been corrupted so the computer can’t decipher what’s on the card. Recovery software can not only contend with that issue but it can also help if you accidentally delete an image from the card or if you reformatted the card before uploading it. Photorescue is my current favorite. The company guarantees that if you download the test software and the demo previews the pictures, the pictures will be recovered with the full program or they’ll refund your money.

The most common cause of memory card failure is a loss of power to the card while it’s being read or written. Really low batteries in your camera could cause this to happen, but more commonly it happens when photographers try to change cards too quickly so that they can continue shooting. If you open the door to the memory card chamber in your camera, and remove the card before the writing from the buffer was completed, you may corrupt the card. Many cameras have a little light that indicates when the camera is still writing. You have to wait for it to go off. A few recent cameras have a safety built in that stops the writing process as you start to open the memory card door.

Recently I had a memory card failure occur on two different cards that were in two different cameras. Photorescue was able to recover the images, but I was at a loss to explain why two cards that I’ve used for months suddenly became corrupted in two different cameras. I knew that these cards had not been prematurely removed from the camera. The culprit turned out to be a faulty USB port on my computer. The port works erratically, and had a power interruption while reading the contents of the cards. Since I switched and use the USB ports on the back of my monitor, I’ve had no more problems.

But what about the cards? Are they still reliable? The answer is that with this type problem as long as you reformat the card in the camera (which you should do routinely anyway) the card should be fine. And mine have been. (Make it a habit to eject the card using the dialog that appears in Aperture when the Import is through, but don’t reformat the card there.)

Occasionally there are other types of problems with cards where the card is readable but certain images are corrupt. Software can sometimes help in those cases, but not always. Cards themselves can occasionally develop problems. After I use recovery software, I reformat the card and shoot some test images. If everything is OK then I continue to use the card. However if the software can’t recover the images, or the same image corruption happens again on the card, it’s time to replace the card. Companies such as Delkin Devices and San Disk offer different warranties and may replace the card, if you have previously registered them and get an RMA number. You’ll need to check your card manufacturer for their specific policies.