Hmm, might be worth checking out. I use a 4Gb CF card, and 32Gb (previously 16Gb) SD card. I cannot recall having problem with my 4Gb SD card, so maybe there is something here. But I get this problem even when I have only used about 1.5 Gb of the SD card, and plenty of space left on both cards. Deleting some files on the SD card seems to temporarily solve the problem. I have not installed the latest firmware, there was only one update right after the release, with some minor changes that should not be relevant.