This might be a good one for our support team--you can send a request to firstname.lastname@example.org
To get a faster response and resolution, you may want to include the following information:
1. When connecting to Tableau Server through the iPad app, please try adding http:// in front of the server name (or https:// if SSL is being used).
2. What version of the iOS is running on the iPad?
3. What version of the Tableau app is being used? (You may wish to upgrade to the latest app version and confirm the behavior there)
4. Screen shot of the error message you are receiving.