I found with my version of Avid MC3.0 that some of the EMP files went to the wrong location when installing under AE CS4. If you look in you AE plugins folder there is an AVID folder. Inside that folder there should ONLY be the EMP.aex file. When I installed mine there were a few .dll files that got installed there. Those .dll files should be moved to your “Support Files” root folder. Then when you load up After Effects choose “Edit->Preferences->Avid External Monitor Settings. and chose if you are pal or NTSC.
That should do it!.