It sounds like the 500GB drive is not formatted properly. In order to boot an Intel Mac, a drive needs to be partitioned GUID and formatted HFS+ journaled. Neither SuperDuper or Disk Utility is going to check the partition scheme - they will just schlep bits as long at the target drive is mounted and writable.
The symbol you are seeing is the "Prohibitory" sign, which indicates the EFI attempted to boot the selected volume, but there is a damaged or missing low-level file. See the following article for details:
http://support.apple.com/kb/TS1892