Hi, I'm Robert and I'll be helping you with your computer question.
it is looking for the password ***** the email account that you set up to share calendars
do you know what email account that might be and what the password ***** ?
if so try that
if you remember the email but not the password ***** can go to the webpage for that email and hit lost password
if nothing else you can go into settings / mail /
and delete the mail acount that isnt working so it will stop throwing up the message.