Q: cannot connect after update

If the notice you received is about an error with Apple's Activation Servers,

There is a known issue/glitch with Apple's activation servers.

Apple, I believe, has acknowledge and recognized this issue with activation server difficulties with certain iPad models and have stated that they are working on this issue and that it will be resolved as soon as possible.

Hopefully sooner.

It is the antivirus and advertising blocking apps that are causing these issues. Casperski, disconnect , etc are being blocked from apple servers. Delete these and you will be able to connect.

Apple has issued a solution to the activation server error, but it has not been successful for every iPad or iDevice affected.

If you can’t activate your iPad 2 (GSM model) after you update to iOS 9.3 - Apple Support

You can try this fix, but if it is unsuccesful, Apple is working on another new solution that should be coming early this coming week.

OR you decide to wait it out until Apple computer/ software engineers can figure out a better solution.

It's up to you.

Good Luck!