Now, following a tip from BDAqua on the Apple forum, I have re-set the P-RAM on the MacBook, and this enables me to start from the external drive. I grabbed the chance to activate and register my PS (again). Now, I want PS back on my main volume in my customized working environment. Would anybody know what I should do? De-activate and un-install from the external volume? I mean this is required if one wants to install PS on a different *computer*, but is it necessary/advisable just for a different *volume* on the same system? Could it do any harm to do it? Hening.