I Carl, I'm sure that this is a double post but I couldn't find the original conversation... ages ago the active careers were a bit bugged when you had two sims in two different active careers. The bug worked like this.... the first active sim would go off to work say at 9am and if you joined them... the second sim whose active career started at 10am would NOT go to work and would lose career progression as the game treated that sim as playing hooky.
Long story short... this bug is now solved and the later starting sims will now go off to work even when you are with your first sim actively.