This issue has been fixed on MCCC.
Make sure to update to the newest hot fix.
Please use the following threads if you have further issues (if you are not using mods)
Hi, I'm back with another update. So the suggested thing to do was to remove MCCC (which I had installed too) and after I removed it, I got the prom pop-up to go (I reloaded a game right before my Sims were set to go). With MCCC, I didn't change any of the settings apart from population settings (for more Sims to spawn on the lot). Not sure if that is relevant but there you go.
For other things, I do play with mods and I made sure they were all up to date and that I wasn't (ironically) getting errors from MCCC. If you have outdated mods, for those who don't know, the past update was a huge update, and broke a lot of mods, and you should remove all mods/update them/remove broken mods, and *very important* clear your cache (localthumbcache) after doing so.
I hope this might help some. For those who don't play with mods, and are still getting the error, I'm not sure. Also, I'm playing on Normal life spans since the update broke long life spans.
