Custom PHP code differs from Devel's one

Hello,

I'm facing an issue which is quite boring since the result displayed into Devel's PHP executer differs from the results of the Custom PHP code. What I want to do is sending private messages (thanks to privatemsg module) to certain users that I can't select with privatemsg Rules integration.

To send a new private_msg, we have to use the function "privatemsg_new_thread($recipients, $subject, $body)".

So I have to write a custom PHP code which is (I made it very simple) ; this one works in Devel but not in Rules.

$recipients = array(user_load(1));
$subject = 'hello';
$body = 'ok';
privatemsg_new_thread($recipients, $subject, $body);

When i write this ; it works with both modules

privatemsg_new_thread(array(user_load(1)), 'hello', 'ok');

Is there a problem with loading variables or sth ?
And i don't have any error log...

Any help would be highly appreciated !

Thanks in advance