FS2004 will not load any more aircraft

After I downloaded the c-5 translaod, then the agusta 109 package it would not allow me to load any other aircraft. All installer packages for every aircraft I try says installer damaged. I deleted AIR installer from adobe and reinstalled it. Nothing yet. I am open to learning so if anyone can help it will be much appreciated.

Stay away from installer packages as tempting as they may be. Learn to install manually and you'll save a bundle on crash-helmets you'll need when banging your head against the wall.