the file defining contacts/sources %application%/lib/api.php is not readable

[youx]

Hi everybody,
I've got this error when I try to access the adress book on imp 3/mysql.

I verified the file is right in this place (horde/imp/lib/api.php) and that
it is readable but I can't find where this file is required. Is there any
particular config to change to indicate the right path to api.php ??

Thanks
Loic