It's hard to say without actually playing with the card. Some of them have hidden folders on them from the factory, like trash folders. I have seen some that have more than one partition(2 1GB's). Make sure the hidden folders are set to be shown in nautilus while viewing the card, and see if there is something hidden on the card. If not, I would use the partition manager to reformat the whole card and see if you can make one big partition. It could be vfat, fat16, fat32. Just see what format it is in before you erase it, so you will know what filetype to reformat it in.
"The only thing necessary for the triumph of evil is for good men to do nothing." Edmund Burke