Check out your account on tivo.com; you should see both TiVos under your account.
To do this, click on the "Manage My Account" link on the left side of the main tovi.com page. (If you don't have an account, first click on Register under "Create an Account" and create a tivo.com account.) Log in, and you should see the TiVos assigned to your account. For each TiVo, if it doesn't say "Transfers ALLOWED" under "Settings", you will need to click on the "DVR Preferences" link on the left side of the page, and then check the "Allow Transfers" checkboxes. (You can also give each TiVo a name.) Last, be sure to click "Save Preferences".
It may take a while for the information to be processed and handled by each TiVo. (Overnight should work if both TiVos are connected via broadband and not a phone line.) First you should see the assigned name for the TiVo show up under "System Information"; then you should see the MAK under "Media Access Key". Once this happens, all should be fine.
The software version shouldn't matter for any of this.
(not the 'other' Juan)