After following these instructions of this excellent "Complete guide to upgrade to Twonky 7 version (My Book World Edition White Light (I or II) ONLY)"
I decide to purchase a licence KEY.
Actually there is an offers to purchase a key
Twonky Server :
$19.95 => $9.97
€14.95 => €7.47
So, if you don't have a key, i think it's a good deal.
Other news : New Release - Firmware Version 1.02.14 for the My Book World I & II (5/14/12)