Do you have wget installed? Its used by the bot for establishing the ssl connection to mt. gox.
Try "whereis wget" - if it cannot be found you need to install it using your package manager. ("yum install wget" or "apt-get install wget")

Also your OS maybe prefers an absolute path

If wget *is* installed and it still doesn't work try changing the lines

   $a = exec ('wget -qO- --no-check-certificate https://mtgox.com/code/data/getDepth.php');

   $a = exec ('wget -qO- --no-check-certificate --post-data "name=' . $username . '&pass=' . $password . $post_data . '" https://mtgox.com/code/' . $scriptname);


to

   $a = exec ('/path/to/your/wget -qO- --no-check-certificate https://mtgox.com/code/data/getDepth.php');

   $a = exec ('/path/to/your/wget -qO- --no-check-certificate --post-data "name=' . $username . '&pass=' . $password . $post_data . '" https://mtgox.com/code/' . $scriptname);