Sims 3 error message

Hi I purchased the Sims 3 last November and since then I have had no problems with it atall, I have also purchased several extension packs such as pets, late night, seasons, supernatural and townlife, and everything was fine until when I tried to log onto the Sims 3 seasons last week and it keeps coming up with a error message telling me I need to activate my game but I have been playing it for months? It asks me for the long number on the back of the instruction manual which when I type in it says its not the correct number for the Sims supernatural, but its the Sims 3 seasons im trying to play, the correct disc and everything is in the harddrive, but it will not let me play any Sims game now. I have also lost the instruction manual for the Sims 3 supernatural. If someone could get back to me ASAP that would be brilliant.