Why is the student unable to fill out an online expense form?

Listen to a conversation between a student (S) and a university travel administrator (A).
S: Thanks for the list of travel agencies. This will really help if I get a chance to go to another conference, but now my question is: you said that the university doesn’t pay for everything, doesn’t cover all the costs of school-related travel.
A: Nope, we do cover the cost of the conference itself, the registration fees, but university policy is that we only cover up to a certain amount of travel expenses. We calculate the average cost of traveling to a city, the average cost of food, lodging, etc., and are willing to pay that much back to you.
S: OK, so how do I find out what the average costs are?
A: Well, on the travel office’s Web page you’ll find a chart with a bunch of cities. Just find the columns for the city that you’re traveling to, like Philadelphia, that’s where you went, right?
S: Yeah, the Eastern Literary Society Conference. It was... I went to hear some presentations, you know.
A: Ok, so the chart will tell you how much the university will cover for trips to Philadelphia. There will be a column for food, one for transportation, one for hotel, but I’m guessing that...
S: Yes, since Philadelphia’s only an hour from here and the conference was just one day, I guess that’s why I wasn’t overly concerned about the expenses, but I did take the train in and of course I ate lunch there. So could I have a copy of the expense form? I’ll need to fill it out.
A: Sure, but it’s quicker if you do it online. That way your information goes directly to the travel office. We’ll be in touch later if we need your receipts.
S: Ok, I already tried that, but the system wouldn’t let me download the form.
A: Really? That’s strange.
S: Yeah, it kept asking for my... for a preapproval number.
A: Ok, the number your department gave you when you completed the preapproval request.
S: Preapproval request? I didn’t know. No one told me about a preapproval request.
A: That’s why you’re having trouble. See, the policy is that your department has to preapprove you for the travel, so that we, the university travel office, so we know you’re doing legitimate school-related travel. We can’t be reimbursing people for their personal vacations now, could we?
S: Well, how was I supposed to know? I mean, my professor only asked me like two weeks ago after someone else canceled.
A: Oh, well that’s it. That student probably filled out a preapproval request. Your department can probably update that form with your information. Then it’ll show up under your name instead, and you can do the online form.
S: Oh, really? Let me talk to them and see what I can do. I’ll come back to you if I have questions after that.
A: Ok, good luck with that.
S: Thanks for your help.