Ajax is undefined

I can not get my game to play. I have sims 3 and I am running it on windows xp. It just tells me there is a microsoft runtime jscript error: 'ajax' is undefined and asks me to debug but when I do it shows me a read only file and I am not sure how tro fix. I tried bypassing the launcher but to no avail. I get a black screen and my game stops responding.