Invalid php exec () command permission

I have a C ++ executable "skypeforwarder". skypeforwarder works if I use the command line in the terminal on Mac: henry $ / Users / henry / Desktop / skypeForwarder / skypekit-sdk_sdk-4.1.2.20_793394 / examples / cpp / tutorial / step3 / skypeForwarder

sh: /Users/henry/Desktop/skypeForwarder/skypekit-sdk_sdk-4.1.2.20_793394/examples/cpp/tutorial/step3/skypeForwarder: Permission denied

But it always issued "allowed permission" if it was called in php exec ();

<?php 
echo exec('whoami');

$output = null;

$execBuild = '/Users/henry/Desktop/skypeForwarder/skypekit-sdk_sdk-4.1.2.20_793394/examples/cpp/tutorial/step3/';
$execBuild .= 'skypeForwarder';

$n  = exec($execBuild, $output); 

I searched a lot. The problem should be the php / browser resolution issue on the web server. I also tried changing the owner of the file:

-rwxr-xr-x  1 henry  staff  1212716 19 Apr 11:23 skypeForwarder

to

-rwxr-xr-x  1 _www  staff  1212716 19 Apr 11:23 skypeForwarder

It still doesn't work.

I installed apache in my mac according to http://foundationphp.com/tutorials/php_leopard.php