first of all thanks for the great plugin!
I just noticed that in version 2.01 of the plugin the large image size settings don't get saved any more (specifically I managed to untick the box, and it saved, but trying to tick it again and save fails).
I've had a quick go on a vanilla installation of the plugin on another blog of mine, and can reproduce the problem there as well...
While I'm not 100% sure I think this bug only got introduced fairly recently. Other settings, such as the new video thumbnail size work perfectly fine.