I am also experiencing this issue. Started new game after installing the 'Get to Work' expansion. Have the Outdoor Retreat expansion installed too. I have never installed mods or custom content for this game. I send samples off and do not get anything back. Currently work the science career and always join my Sim.
Even when I stay on lot during the weekends off, I am only yet to receive bills and nothing more. Received 2-3 back from geo when first started. Didn't have this problem on previous saves before 'Get to Work' expansion. Don't want to cheat in the game either (even just to get remaining elements) as that kind of defeats the point of playing.
