Are you downloading the latest version (ignore all the others) from here:
http://sims2pack.modthesims2.com/index.php?page=3MTS2 (which hosts the download) has been having on-again, off-again service and download glitches all this week, so it may well be that you just have to wait a bit until they are back up to speed.
Also, try turning off Windows Defender before attempting to install it -- Defender is really not necessary and is
very intrusive, and turning it off is generally a Good Thing anyway -- it
mightbe flagging Clean Installer as spyware or malware (which it is not).