Memory card won't save a game with 64,000KB free space

[Stardarkening]

I'm playing a game on the PS2, and when I go to save, which only requires 90kb, it says there is no room on my card, when the browser says there is roughly 64,000Kb available. I also put in another card in the second slot, and the game does not even read it, when the browser says it is there and has ample space to save this game also. I don't know where to begin. Help would be greatly appreciated.