steam missing file privileges issue

@gameatea  Please run Steam as an admin, as in, right-click on the Steam shortcut and select "Run as administrator."  If that alone doesn't help, run it as an admin again, right-click on the taskbar and select Task Manager, make sure you're looking at the Processes tab, then find the entry labeled "igfxEM Module" (you'll have to scroll for a bit).  Click on it and select End Task.  Now try to download the game again.

By the way, you say you bought "CE."  Do you mean you bought the complete edition of Sims 3, or some other game?  If it's the latter, there might be a better section to ask, but this thread can be moved easily enough.

Thanks to both of you, will follow every solution you suggested to me. and Thanks responding so soon.

Turning off antiviurs and firewall shield helped me twice with this issue.