suggest spoofing your version to 3.74 in Henkaku settings rather than performing a full official update if you wish to maintain custom firmware while staying online. Device Setup Password to sign back into your account after the update? PS Vita System Software (US)
Your Wi-Fi network blocks PSN services or the Vita’s SSL certificate is outdated. ps vita system software update 374 download upd
Move PSVUPDAT.PUP into the UPDATE folder. suggest spoofing your version to 3