Which EPs do you have? Namely, isn't it BV where you can start choosing which townies to age up along with your sim, and could this be in any way related?
I have all the expansion packs.
Also, have you been selecting "Grow Up" by clicking on the sim each time, or have you tried sending them to a cake and seeing if it'll work that way? Have you tried leaving them to their own devices and seeing if 6pm takes care of the issue itself?
I haven't tried that yet, but I plan to when I get some time.
Is it the same twin each time who causes the problem, or is it whichever one is going second at the time?
The problem is with the sim - after restoring the game I had her try to age transition first.
Oh, does the 2nd grow-er-up-er have any items of custom skintone or hair that might be throwing an error when they try to switch to the next level's? When you tried growing up in debug mode, was there any error log generated therefrom?
Both sims are aliens.
(therefrom. a word? dunno. but I think I like it.)
It is now.