Hi there,
I have been having the same problem too. Only, my sim has not been able to attend classes from the very first time I loaded the save. My sim was also not able to attend the meet and greet the very first day. The message popped up for him to attend and for a split second the action appeared in his queue but then every sim on the lot reset and I was given a bunch of popups from error trap. These two events seem to be related - it couldn't possibly be a coincidence.
I have tried removing my mods (I double checked that they were all updated to the appropriate patch). As most of my mods are Nraas, they were updated rather quickly (for reference I use Master Controller, SP and its add ons, Error Trap, Overwatch, Porter, Woohooer, Portrait Panel and Decensor). I also ran my save vanilla and that had no effect. I tried sending my sim back home and then back to uni but once again, no effect.
The very last thing I tried was sending a sim from a fresh save to university. And it worked! I'm happy I got this much figured out but it's kind of lame that I won't be able to send my legacy family to university unless this problem is sorted.
My computer is more than capable of running The Sims and all of the expansions, so I doubt it's a problem with performance. I have all EPs and SPs to date.
At this stage, I can only imagine that this bug has to do with EA.