headdihall -
This error may lie with UPS. I've had a few numbers that come back as invalid when I first enter them & have come to find out that the problem usually is that UPS hasn't had the time to get the number in their system or they haven't picked it up from the warehouse yet.
You might want to double check the number after a few hours to see if it's in the system.
HTH!
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katc@birdmail.com