The mail server imap.gmail.com is not responding
1. Close the mail app on your ipad
2. Go your Mail Settings on from Google’s web mail client (It’s under the Forwarding and POP/IMAP tab) and make sure IMAP is enabled. If it’s not, enable and save. If it is, disable, save, re-enable, and save again.
3. Relaunch you mail app. This worked for me.
If it doesn’t work, the next step is deleting the account on you iPad, and adding it again.