This is a bug in the leaked 2.2. Here's what I believe fixes this:
Go into your SDcard/DCIM/Camera folder and look for the last picture you took. Delete it, and then try opening the app again.
If I ever got this bug where I couldn't open the camera app on 2.2, it was because the last picture I took was bugging out the app somehow. So deleting it resolves the issue.
You could also reboot your phone and that should fix it too. But thats more of a pain to me.