I'm having the same issue with my magic sim family. Reading the thread, it might be due to a clothing change? I'm on a park spot with no mannequins at the moment, but I've seen errors occur a few times now. I noticed from MCCC and they sent me over here. I only just downloaded that mod, so I'm not sure how long it's been occurring. It doesn't seem to affect game play any.
I had the same issue. My alien sim had a club gathering and the last exception triggered when the human tried to change clothes in order to work out. He still worked out, that was fine, but he was still in his regular clothes. I did not have any mannequins on my lot as it was my residential lot. This was the first time I got the error and I cannot recreate this issue with my sim.
a month ago
I got this when i was making an occoult club. The Mccc help discord has told me it "has been attributed to Club Gatherings and Occult Sims in particular. Mannequins on retail lots may also be a source of this issue."