Undefined index: shippable in uc_ups_product_alter_validate() (line 134 of ubercart/shipping/uc_ups/uc_ups.module)

Actually I seem to get this error every time I save a product node as well.

The line it complains about is:

if ($form_state['values']['shippable'] && ($form_state['values']['shipping_type'] == 'small_package' || (empty($form_state['values']['shipping_type']) && variable_get('uc_store_shipping_type', 'small_package') == 'small_package'))) {

Not sure what the problem would be with that. The field is definitely set in the database as a 1. for products that are producing this error upon save.

Attached is a patch that gets rid of the notice, but I am not sure if it is the correct fix.

The main reason I did that in the patch was because I saw the same type of test done in ./payments/uc_paypal/uc_paypal.pages.inc at line 348 and 358 and thought maybe it needed to be in there.

You must be right that it is the fault of a contrib module. The modules that I use that relate to Ubercart are uc_attributes_in_cart, uc_fedex, uc_feeds, uc_tracking, and a small module I made myself that adds an empty cart button to the cart page. Disabling these one at a time along with a cache flush did not seem to affect the notice at all.

Any tips on how I might be able to track down how I am losing the shippable key? Would it have to be something else that is using hook_form_alter on the product_form?

I was mistaken. It definitely only happens on Product Kits. It showed up when I saved products only because those products were part of a kit which was also being updated at the same time. Updating the issue as I think this is something I did. Will report back later.