Lags & Invisible, Frozen & Stuck Sims --> Post here if you have the issue.

Crinrict, thanks, I think I'll try ErrorTrap.

Edited later: Have been reading about other mods. I might also consider downloading the alternative StoryProgression, which sounds much better than EA's and more to my taste. Seems like I've gone from being completely anti-mod to a Twallen groupie! I can always delete the mods if it doesn't work out or I become baffled.