I have just upgraded to Drupal 6.19 and Ubercart 2.4.
Now checkout isn't working. When I click on review order at http://royalgems.co.nz/cart/checkout, it just redirects to the same page. If it enter http://royalgems.co.nz/cart/checkout/review, it also does the same. I do not get any error messages or log entries. I installed the uc_optional_checkout_review module, but when I click on review order the same thing happens.
When I upgraded, update.php got stuck updating ubercart, but I deleted and replaced it and it didn't update or provide an error. Could this be the problem? Everything else seems to work ok.
Update: I am currently doing a fresh install in the hope that works and I can add all my products etc later.