SOLVED using ajstarks's solution for SD Cards that have been mounted on Mac OS (which mine had, to make a backup image). Specifically, removed the ._.Trashes .Trashes/, .fseventsd/, and cruft that OS X put on the card, and all is well
Thanks, that's a relief!
ajstarks wrote:I too had the persistent red light problem. Note that I was loading my images from Mac OS X and the SD card failed to load. After checking the (brand new) SD card on Windows, I discovered and removed the extra ".dot" files that Mac OS X leaves on the disk. After manually removing these with Windows,