Hello all,
I added these two lines
$conf['davstorage']['params']['driverconfig'] = 'horde';
$conf['davstorage']['driver'] = 'Sql';
to
/etc/psa-webmail/horde/horde/conf.php
and the errors dissapears. I had a look in /var/log/psa-horde/psa-horde.log - this says that the error occurs in...