On the newest update my usual 35-45 fps has dropped to a 5-10 fps.

What is the reason for this and how can this issue be resolved?

put -d3d9 at the end of your shorucut.. of the game

Still have FPS lag, thanks anyway.

Use -d3d9 startup parameter, which will disable d3d9ex extension.

 

What is meant by this?

Create a shortcut to LaunchIW4M.exe, right click it and select "Properties". At the the end of the "Target", add -d3d9 and your FPS should be as good as always.

Make a shortcut for it on the desktop and try again.

Uh, put the parameters to LaunchIW4M.exe in your IW4M folder, then run it with that.