hmm, very unusual, when you have formatted the card have you done this in the Ricoh?
I'd give that a go if it was formatted elsewhere.
Also I often check the SD card with disk manager in XP or Win7 to see what type of partition and format them there.
I think they should be FAT32. I have had issues with speed of cards and various brands.
These guys offer a free (for home use) Partition manager, http://www.partition-tool.com/personal.htm
You could use it to help check the card and reformat it but for a final format I would do that in the camera.
My Sigma DP2 is very fussy. The current card takes ages to write a RAW.