To restore the image, I usually point to
Memory Upgrade Mod Guide. They are for the Glo, but the basic steps and tools are the same for all the devices. It is also Windows centric, but there is some discussion of doing it on a MAC in the thread.
It does sound like the imaging is not being done correctly. I am sure I have seen reports of using Disk Utility successfully. But, it sounds like there is a problem with one of the cards. As one card works in both, and the other card works in neither, it suggests the card is failing. Have you tried a new card?