Select the top level node called Unity-iPhone in the left tree view (the one with the blue item).
Select Automatically manage signing
Select your team (now the error message should appear)
Go to Build setting in the tab
Find the Group called "signing" in the structured table
Change the values from "iPhone Developer" to "iOS Developer"
Switch back to general (the error message should now disappear)
Your project should compile now and should be runnable on your iPad or iPhone.