Remove the add item button in custom module magento

 Simply add $this->_removeButton('add'); line as specified below in Block/AdminHtml/Module_Name.php file

public function __construct()
{
$this->_controller = 'adminhtml_yourmodule';
$this->_blockGroup = 'yourmodule';
$this->_headerText = Mage::helper('yourmodule')->__('Module Manager');
parent::__construct();

$this->_removeButton('add');

}