Okay, I'm going to put the solution I found here just in case anybody needs it. I realize that my problem was quick, but it was the most frustrating thing. I'm not too entirely sure what I did that solved this, so I'm just going to put my whole process here. I was at University, so I figured that might be part of the problem. I went to my home town, which just happened to be Isla Paradiso. I didn't edit anything there, I just went back to University. Nothing seemed to have changed with my problem at that point, so that's probably not what fixed the problem. I had reset all the sims in University earlier, so none of my sims were in a bad mood. I then shift-clicked on the mailbox, and set the needs to static. I thought that this might be able to hold me over until my problem was solved. So all the mood bars of my active sims went all the way up. This is probably what happens when you do that, but I found it suspicious. So I set the needs to dynamic again, and bam. I now can move the bars. This is a rare problem, I suspect, so not many people will need this. But just in case, here is my solution.
