There a mistake in how you're calling your renderer. Try this:

$this->addColumn('Vendor Code',
            array(
                'header'=> Mage::helper('catalog')->__('Vendor Code'),
                'width' => '50px',
                'renderer'  => 'ailin_orders/adminhtml_sales_render'
        ));

There's a mistake in how you're calling your renderer. Try this:

$this->addColumn('Vendor Code',
            array(
                'header'=> Mage::helper('catalog')->__('Vendor Code'),
                'width' => '50px',
                'renderer'  => 'ailin_orders/adminhtml_sales_render'
        ));