The product kit module passes it's entire $form_values array to uc_cart_add_item() when the Add to Cart button is clicked. This array includes the product's nid and quantity which is passed to uc_product_add_to_cart_data() when each individual product is added to the cart. That would be the source of the error.
Use this:
<?php
$data = array('products' => array(
$nid1 => array('nid' => $nid1, 'qty' => $qty1),
$nid2 => array('nid' => $nid2, 'qty' => $qty2),
//... etc.
));
?>The 'module' is included as part of uc_product_kit_add_to_cart() so you don't need to specify it when you're calling uc_cart_add_item() on the product kit. Also, the "null, true, true" are the default values so you don't need to specify them.
Joined: 08/07/2007