absmith, I had the same problem (after reading your post I checked my MRJAppBuilder when I got home).
I remembered that I had a problem when I installed the Dev tools before, since I was ever so watchful of the install log. There was a line that said that MRJAppBuilder couldnt be deleted because I had version 10.x.xx and the version that was trying to be installed was 1.something.
Anyhow, I deleted MRJAppBuilder and reinstalled the Developer Tools, and the new MRJAppBuiler 1.1.x was installed and works fine
I guess it was a version error in the way the Developer Tools 10.0.4's MRJAppBuilder was labeled, and then later how the new version with the Dev Tools 10.1 were labeled.
Anyhow, now everything is nice and kosher
-Esteban