I bought the sims 3 supernatural in the store at best buy and I purchased the sims 3 on steam about a year ago. And now I want to install the game supernatural to my sims 3 on steam but how do i do that?
afaik i know only steam versions work with steam origin and or disks do not work with steam , so basically what is happening there for you is the orign download of town life is looking for your the sims3 base game either a disk or origin download it does not recognise the steam version as the default paths are different so the only way to get it to work is to which you may not want to do is this get your sims 3 codes from steam redeem them in orign uninstall the steam versions then download and install them from origin
edit to add found the FAQ hope this helpes http://answers.ea.com/t5/The-Sims-3/FAQ-Steam-VS-Origin-VS-Discs/m-p/3135440#M165305
