Hello Milo

db_settings.php of the second installation:

 
$db_settings['category_table'] =       'mlf21_categories';
$db_settings['userdata_table'] =       'mlf2_userdata'; // common user data

Afaik, this modification is not supported by the update routine, i.e. db_settings.php file will be overwritten in an unwanted way.

It might be possible to break the db_settings.php. If, it has to be corrected manually. On the other hand the update script seems to take the value from the settings array. In that case it uses the correct table names.

Tschö, Auge