This check is correct. You have an error in your configuration file.

I created a local config file "imp/config/backends.local.php" and it 
fails to load.  The message in the syslog is: [imp] Failed to import 
configuration file ... on line 379 of "/usr/share/php/Horde.php"

Looking at the code, we see this if statment:

if (!empty($output) && !$show_output) {
                 /* Horde 3 -> 4 conversion checking. This is the only place
                  * to catch PEAR_LOG errors. */
                 if ($log_check &&
                     isset($conf['log']['priority']) &&
                     (strpos($conf['log']['priority'], 'PEAR_LOG_') 
!== false)) {
                     $conf['log']['priority'] = 'INFO';
                     self::log('Logging priority is using the old 
PEAR_LOG constant', 'INFO');
                 } else {
                     throw new Horde_Exception(sprintf('Failed to 
import configuration file "%s": ', $file) . strip_tags($output));
                 }
             }

In the code above, all local files have $log_check = 0, which causes 
this if statement to fail and throw an exception every time.

So I cannot use any .local files because this check causes them not to load.