The error message would seem to indicate a font conflict.
Try removing all non-system fonts from your OS, and attempt relaunching.
Thank you for the sugestion, Steve. I'll try that when I get home (The crash problem isn't on this PC I'm working right now). Is any simple way to recognize and remove the non-System fonts from Windows 7?
Here's a list of the fonts installed with the Windows 7 Beta.
Alternatively, if you've knowingly added fonts after installing the OS, you may just want to remove the ones that you've knowingly added.
If you haven't added any fonts, you may want to try resetting the prefs by holding down ctrl+shift+alt while launching AE.
Sorry. Just arrived home. Done what you said. Nothing changed. The error message says: After Effects warning: Unknown BIB Error. Cannot access font, CT, 0 (83::3).
The curious thing is that when I restart Windows 7 and start After Effects it opens without a problem. Only when I close After Effects and try to open it again it crashes.
Don't know what else to do. Sorry......