The latest iOS 9.3 update from Apple has a glitch which has locked many older Apple device owners out of their devices. Apparently after the update, iOS is asking for userid and password for the Apple accounts to reactivate and users who have forgotten those details cannot access their accounts anymore. The issue is prevalent with iPhone 5S and older phones as well as iPad Air and previous variants of Apple tablets.
Apple is scheduled to come up with an update that will bypass the account activation process allowing users of older devices to log in. Another workaround provided by Apple is to log into the iCloud account after connecting the phone with a computer and go to Find My Phone. After entering the current Apple ID into iTunes the issue should be resolved. However if the current Apple ID is not known, then contacting Apple support is the only option.