Type 11 error is just a general exception. Something wrong happened some place, and it just reported Type 11. When Apple moved from 68k to PPC, as a temporary measure most errors were simply called Type 11. As the OS matured on PPC, most of the error codes were fixed. The problem is that even though the error codes were corrected, it didn't make any of them (especially Type 11) easier to fix. There's something wrong with the system software you're running, or there's an issue with your hardware (less likely). Are you booting from a CD? If it's still trying to access the drive when you're booting from the CD, hold down the C key, or, alternatively, hold Delete+Option+Command+Shift to bypass the internal drive completely. See what you can do with that.