After Effects CS5 and Premiere Pro CS5 both can crash due to a conflict with the Joesoft Hear audio enhancer.
We've just gotten confirmation from Joesoft that they've released a beta version of Hear that doesn't conflict with After Effects CS5 and Premiere Pro CS5. We're recommending that our customers who also use Hear install the 1.0.5b2 (build 490) beta version of Hear.
Let us know on this forum thread whether this solution works for you. We on the After Effects and Premiere Pro teams will monitor this thread for feedback, and we'll make sure that the folks at Joesoft get the information that they need, too.
After 2 days trying to get AE and Premiere past the mediacore initialization message, I finally stumbled on this little message. Updating Hear definitely solves the problem!