@adamphaneuf if enough of the information regarding the expense matches another expense you could get the duplicate transaction message. It doesn't necessarily have to be the same day.
Usually the duplicate exception message is denoted by a yellow triangle. If the message is the the yellow triangle, you can still submit the expense report.
So, I looked at your expense report. The duplicate message isn't preventing submission. It is the message in the screenshot below regarding overtime or weekend meals. This will need to be corrected.