To sign in to PSN, you are now required to use a Device Setup Password . This replaces your standard account password on the handheld to provide an extra layer of protection (similar to 2-Factor Authentication).
The most recent widely available firmware—and the last stable build for most non-developer units—is (often colloquially searched as "374" or "3.74"). If you have just dusted off your Vita, purchased a used model, or accidentally let your auto-update lapse, you might be searching for the PS Vita system software update 3.74 download upd process. ps vita system software update 374 download upd
Database conflict or faulty memory card. To sign in to PSN, you are now
instead of your regular account password to improve security. Account Management Removal: To sign in to PSN
Via Content Manager Assistant (PC/Mac)