If this is a pre-owned unit be sure to update your Sentinel software AND Firmware before you start programming. I would assume that in a new unit it would have updated software.
In theory, that would be correct. However, the database included in the initial installation, as well as in the scanner, is probably several years out of date. So, when installing Sentinel for the first time, update the database after installation, as well as use Sentinel to write that update to the scanner.