Well, the only thing I did specifically was:
go into your system hard drive, mine is ‘Macintosh HD’ to this folder:
Macintosh HD/Library/Quicktime/
and drag out the 2 Avid Meridien components to your desktop (don’t trash them!):
AvidAVUICodec.component
AvidAVDJCodec.component
once I did this After Effects started up again. This worked for me, I don’t know if it will for you but its worth a shot.
The only thing is when you want to create an Avid Meridien quicktime you need to drag those 2 components back into the quicktime component folder again.
So you won’t be able to render a Meridien quicktime out of After Effects, but render out one at Animation Codec and use QuicktimePro to export an Avid Meridien quicktime after you drag the components back in.
Let us know how it goes, I am curious if this is just me thats running into this Meridien thing.