Hi Roberto,
Yes the uninstalled copy on the XP box needs to be deactivated. Simply uninstalling will not show up as a deactivation in our licensing server. Unfortunately there is no way for you to be able to do that yourself on WinXP. I talked to our licensing team, and if you send an email to sales@camerabits.com they should be able to handle this for you and make it possible for you to get get that XP install deactivated.
Thank you,
-Mick