Strange error with compile_dir and cache_dir properties

Hi,

At the initialisation of the page I redefine directories properties.

If I do
$smarty->template_dir = "/include/template/templates/";
$smarty->compile_dir  = "include/template/templates_c/";
$smarty->config_dir   = "/include/template/configs/";
$smarty->cache_dir    = "include/template/cache/";

it works but if I do
$smarty->compile_dir  = "/include/template/templates_c/";

I have this error : Fatal error: Smarty error: the $compile_dir
'/include/template/templates_c/' does not exist, or is not a directory. in
xxxxxxx/include\php\externe\smarty\Smarty.class.php on line 1102

I have the same problem with the cache_dir property but not with
template_dir and config_dir.

I know that the directories exists


Thanx for you help