Error message: This game cannot be launched. This may be the result of a full iPod.

My iPod suddenly gave me the above error message even though it is an 80GB system and I have used only 20GB of space at the most. Now, my iPod is not being recogonized on my computer nor iTunes. In addition, I can't get this error message to clear off and my music will not play. Any suggestions on how to correct this issue?