C F Card Issues

Hi there. I have had this happen to me twice now with different cards. I am shooting just fine and then I get a message stating that my CF card is full. No problem I just pull out a new one and go on my merry way. The problem is that when I try to download them Iphoto says that there is nothing to import. Even if I delete some photos it still says there is nothing to import. I have used these cards before with no problems until it gets 'full.' I can see the photos on my camera but they won't import. Any ideas on how to get them onto my hard drive?

Thanks for the help!

When you plug the card in, watch your trashcan icon. Does it "fill up"? Perhaps there is a lot of space used up in deleted files?