Seems to be a fairly common problem. I had it happen to me once and all I did was reboot the phone. After it came back on, it gave me the "damaged SD card" error message. I took the card out, plugged it into my laptop and was able to read it just fine, and all my files were still there. Put it back in the Hero and it work fine again like nothing happened. When I Googled that error message, there were many people with Android-based phones (not just Hero) having this problem.