Sims won't go to work after one of the family has graduated.

Out of the blue, once one of my family has graduated the others get the message that it's their work day, but they don't get a carpool, and when I try to send them to work I get the message "it's not your workday until......" And then it is NEVER their workday again. The only way to resolve it is to evict them, save them to the sims family folder, delete the original family and move the copy back in. Which means wasting money buying the house over and over every time someone graduates, and losing friendships with the neighbours. There must be game/family corruption, but why now? I haven't downloaded anything, uploaded anything, changed anything or bought from the store for months. I'm also waiting to see if I soon get error 16 in my new neighbourhood whereas previously I could play a neighbourhood for months and had never heard of error code 16.