Development for the module seems to be mostly at a standstill, presumably due to the developer jumping into Drupal Commerce, yet for the Drupal 6.x users still working with Ubercart, Better Cart Links is pretty much unusable.

Attempting to create a link with Better Cart Links drops the error “Product ID not valid” even when using a valid Node ID.

Anyway, here’s the patch. The issue was product IDs being called incorrectly in the mysql query. The fix is working well for me, but if you have any issues let me know.