Thank you to everyone who has reported the crash bug in beta-8. I found the crash this morning thanks to some helpful bug reports (technical explanation: boneheaded code on my part) and the fix should be in the next beta.
Also it looks like QuickTime 7.0.4 isn't compatible with the AC3D x-plane export plugin. This makes no sense to me...I spent over an hour remotely debugging on a user's machine (thanks Peter!) and came to the conclusion that something is borked deep down inside a library. Somewhere. Maebe. I'll try to get this resolved soon but since I do not have an OS X 10.4 machine, it may take a little bit. In the meantime it is possible to go back to QuickTime 7.0.1.