If you are using the Thick Client to get Book Numbers for UPS, sometimes you will find that this does not work properly. What might happen in these cases is that the Book Numbers do not show in a timely fashion or vanish.
This would seemingly be a side-effect of performing a second 'Add Shipper' function, which might wipe out those values.
What you will want to do is, first, just wait awhile and do a 'Check Mail' function every now and again. If you search through the PLD folder you should be able to search against "rad" and pull up all of those files that start with "rad". Limit those results by the day that you originally performed the "Add Shipper" and open those file(s) 1-by-1 until you find the one that contains the information for the UPS Account Number in question. Once you find that file, look mid-way down the listing of items and you will see the Book Numbers. You can then manually add those to the Web Setup.