I recently had a a problem adding a tracking number to a second transaction.

Normally, I have no problem adding a tracking number to multiple sales, I did it less that a week ago. However, one time I kept getting an error saying that I couldn't use the same tracking number for 2 transactions. I solved it by removing the tracking number from the original transaction then adding it again. It may have helped that wen i re-did it, it was less than a minute appart. The first time, when it failed, it was 1/2 an hour apart.