Q: Calendar App keeps asking for my Yahoo password

If I start up the Calendar App in Mavericks, I am constantly asked for my Yahoo Account password.

I enter the password, nothing. So Calendar asks me again, what is the Yahoo Password?

I have deleted the iCloud account from my iMac.

Reset up a new iCloud Account.

Changed the Yahoo Account password.

Trashed Yahoo Mail accounts in settings on iMac and iPad.

Then readded Yahoo Account in Mail settings w new password.

I made a calendar date on my iPad, the iMac immediately showed it.

So incidents are synced.

So why can't Calendar accept my yahoo password? Or do I even need Calendar to open, if all date incidents are synced?