That is an issue with proDAD. Like you, I hadn't used the SAL in a while. When I started it up, it asked for me to activate again. It happened with no problem. BUT.... running Mercalli V6 SAL, I too get the same error message.
Personally, I don't like version 6 - there are no presets like Universal and Rock-Steady - so I continue using version 5 which is the same as version 4 but with some technical updates but no new features.
Oddly, the Merc 6 plugin for MAGIX branded NLEs (but not Vegas Pro) does include the presets.
The few times that I use 6 SAL is because it can do stabilisation better without 'ghosting' that can occur in 5 SAL in some unique circumstances.
You'll need to check that with ProDad, but I think that it can be installed on more than one computer but can only be activated on one computer at a time.