Apple was forced to pull a build of iOS 9.3 for older iPhones after it was found to cause activation problems on the iPhone 5s, 5, 4s, and 4.
“Updating some iOS devices to iOS 9.3 can require entering the Apple ID and password used to set up the device in order to complete the software update,” explained Apple. “In some cases, if customers do not recall their password, their device will remain in an inactivated state until they can recover or reset their password.”
In response, Apple pulled the build of iOS 9.3 specific to these older iPhones. The company patched the problem and has made the update available once again.
Customers who downloaded the faulty version and are experiencing authentication issues can work around them using steps spelled out on Apple’s support site.