[horde] DB Error: extension not found ? help please ...

[Mehmet Fatih Akbulut]

hi all,
i've installed php5-mysql and and i also have "extension=mysql.so" in my
php.ini configuration.
but still i get the error in subject line when trying to configure horde.

>A fatal error has occurred
>DB Error: extension not found
>[line 393 of /var/www/horde/lib/Horde/Prefs/sql.php]

what may cause this problem ?
help please ...

Cheers,
MFA