It's not having your speakers connected, the fix he is telling you about is to plug a headset jack into a speaker port at the back of your PC, as i said it might work but never worked for me. Problem with this error is that are many "possible" fixes and everyone thinks they have the solution but they will only tell you what works for them, told you what works for me, everyone should Google this and try every fix until it works but i have seen these help posts for 7 years now, here are a couple of Google fixes but really everyone should have a bit of savvy and Google this themselves.
http://www.exe-error-fixes.com/iw3mpexe-stopped-working-application-error/
http://ccm.net/forum/affich-132360-cod-4-modernwarfare-pc-iw3mp-exe-has-stopped