It's possible the box is already hacked, unfortunately I've not got round to updating the DMS with the latest version of the patch that does tell us if this is already the case via a similar prompt.
So, let's concentrate on the new DMS for now. The drive you are using for the new DMS... is it a clean drive, or did it have an Operating System on before?
Using the DMS tools, with the new drive in the cradle, click on 'Boot Check'... if it asks you if you want to to put the bootload file on to the disk, reply yes and then try and boot the new DMS in the car. Bring the DMS back, and click on the Boot Check again.
If it doesn't, or after attempting to boot the new DMS in the car, paste the resulting message back here.