[horde] Error : Path of Pear Log

[Horde]

Hi,

By trying to reach the basic Horde directory, I always have this error. 
It also comes when I am in the admin part, outside of the setup menu.

Notice: Use of undefined constant PEAR_LOG_DEBUG - assumed 
'PEAR_LOG_DEBUG' in [...] /lib/Horde/DataTree/sql.php on line 179
Fatal error: Undefined class name 'log' in [...] /lib/Horde.php on line 
111

The latest Log Module is installed :
[root at zapata root]# pear install -o Log Mail Mail_Mime DB Date File
Package 'Log' already installed, skipping

And test.php shows all the Pear modules excepted Log as ok
PEAR
     * Log: No
       Your version of Log is not recent enough. THIS IS A REQUIRED 
MODULE!

I have been told it had to be an error with the internal Log path. 
Could you tell me in which Horde file I have to change the Log path so 
that it be taken everywhere ?

Thanks a lot.

Alex