Hi,
I had this same continual problem with the CalDav prompt popping up and asking for my "Yahoo" server account password, even after I had entered my email account password in the Account Setup page in Settings. I do not use a CalDAV service, so I had no idea why the prompt kept asking me for a password for it. Through some research, I came to find that the root of this problem existed within my Yahoomail account, and not within the iPad's iOS. Here's how I solved the problem: I logged into my Yahoomail account via the iPad's Safari browser, and then, once logged into my Yahoomail account, tapped on my email address at the bottom left-hand corner of the screen. I then tapped the "Options" tab that popped up, and selected " "Classic Mail". You have to do this in order to allow the service to let you into your account settings. Once logged in, go to the "Contacts" tab, located two tabs over to the right of the "Inbox" tab. Once inside Calendars, take a look at the left side of the screen and you should see the heading "Calendars" about 1/3 of the way down the screen. Under this heading, you should see a Calendar name that corresponds to something to do with your name or person with a black check mark in a box to the left side of it. Uncheck this box, as this represents the CalDAV that the prompt keeps asking you to give the password for. Once you uncheck the box, go back to the iPad's Settings, go to Mail, go to Add Account, and renter your Yahoomail ID and password. Blue check marks should shortly appear next to all of your entries here, and you should almost instantly see your email account start filling up the Mail Application. I hope this helps anyone else who has had this problem.
