Why does my USB say, "USB is damaged or unreadable." when I try to load something I saved onto it.?

I recently bought the game NBA 2K11 for XBOX360. On my player mode I found out this way to get billions of skill points on youtube. It involved modding on my USB and so the mod worked and now NBA my player mode is extremely fun. It's been working for about a week now and I try to load my player from the USB but it says, "USB is damaged or is unreadable." Is that because XBOX caught my mod or something because I haven't done any changes to my USB ever since I did that hack.