With @rckoenes 's help I finally found the error after I hit a couple of times when I get the exception. It stops at UIViewController loadFromNibName because the line
[NSStringFromClass([UINewUserAccountViewController class]) stringByAppendingString:@"~iPhone"]
returns a nib name but in the xib file with that name the root view is not a file outlet. After I link the view to file outlet the exception goes away.