Why does my computer verification fail after Apple ID reset?

[iMore Question]

Computer verification fails after Apple ID reset

Macbook Air Yosemite 10.5 (not mine). I tried to activate FaceTime on my bro-in-law's MBA this evening but he couldn't remember the password. We reset the password but the MBA iCloud won't accept it even though we can log onto iCloud via browser. Getting "there is a problem verifying this computer. Reboot and try again" but this makes no difference at all. So the MBA is not connecting to iCloud or any other iApp at all. Any suggestions? Am a bit desperate as he is only here until lunchtime tomorrow. Thanks