Re: Sims cannot enter student union building.

@KalumWhyte  Without mods, the only thing you can do is bulldoze and replace the lot while in Edit Town.  You may need to place a second copy of the lot somewhere in the world before removing the first, then keep the second until after you've replaced the first, so that your sim doesn't lose their class assignments or progress.

If your sim only just arrived in University, the other option is to revert to a previous version of the save and try again to travel.  That will generate a fresh instance of University, hopefully without this issue.

There are mod-related interventions too, if you're interested at some point.