I'm sorry if I am comming across as pro-mod. I do understand and respect why some players might not ever want to use them. I mentioned it here because I had a similar issue a couple of years ago. I played Sims 3 frequently, but then either lost or broke the disk I needed to play it. I was so bummed out about it that I simply took a long, long break from the game. I might not have come back at all were it not for the Steam sale that got me back in. With the Steam version one doesn't need a disk at all since it is a purely digital purchase from EA.
I agee that you are probably correct that the original poster just misplaced or accidently used the wrong disk and it would be very easy to fix just by using the right disk. Still, I do know from my own experience that this isn't always the case.