Ok, I"ll answer. In addition to calling a deviation ticket a "personal ticket home using the 3-day rule", it would appear you are unable to use the expense report system properly.

I did some experimenting with my expense report and got the same message in red that you saw. It happens when you try to associate a seat selection fee with a revenue leg instead of a deadhead leg using the pull-down selections on each expense. The system doesn't stop you from inputting that error into your report, but it does catch it when you view your report. I got the red message to display in my un-submitted report after selecting the wrong type of flight and entering that expense into my report.
So, no one denied you anything except you. Don't submit your expense report with red errors showing. The system was trying to save you from yourself.