I just fixed it installing JBoss manually!
Yes, I was using this site to install!
Did you download archived p2 repository and it work for you? Bits on that update site and in archived p2 repository should be the same.
What is your OS? I want to check it and see if I can replicate it.
Yes, I've downloaded and it worked!
I think that should be the same too. It's awkward...
I'm using Mac OS X 10.8.2
I've verified it under Mac OS X 10.8.3 and it works for me for both Juno and Kepler update sites.
Any other clues? Could you tell some more details like:
1. Was clean eclipse downloaded from eclipse.org used?
2. What kind of eclipse distro: standard or Java EE Developer IDE?
3. Did you add any other update sites manually before installing JBossTools?
4. What are JVM version and architecture?