Please be careful: Horde has introduced a new default setting $conf[‚auth‘][‚lowercase‘] which acts like the auth hook used to do.
This might lead to issues when your default admin account is named „Administrator“.
It is actually a very useful setting. It ensures that any prefs and other profiles also work with case-insensitive backends regardless of how you type the user name.
How to fix?
a) Lowercase all admin names in your $conf[‚auth‘][‚admin‘] settings in conf.php
b) disable $conf[‚auth‘][‚lowercase‘] by setting it to false value.