So, in order :
deactivate your vita
format memory card
format internat memory
restore factory
sign in psn
activate games
download one game only to test in internal mem
try it
If this one work, insert your memory card and reboot vita
finally, copy the game in memory card and try it.
If this...
I don't think this is the cause. I think about corrupted data.
C2-12828 is an error I has and the only solution is to format memory card or delete and redownload games.
Hi guy, it's seems yours games are deactivates.
If you are in a 3.70 ofw, go to your psn account in psn setting in vita and deactive your device in Game category.
Reboot and do the same thing but activate to generate your act.dat (licence file).