I\'m trying to restrict access to our RavenDB to only one user. After altering the settings to secure the DB, I can still access the RavenDB management studio and I\'m not sure
You say you are on build 573? That's very old. According to the release history it was published on 12/15/2011. There is a commit dated 2/22/2012 that says "Change Authorization to return 403 if user is not in group or users list". That's probably a fix that you need.
I would update to at least the last stable build - 1.0.960 and see if your issue persists.
If you're not in a production environment, now would be a good time to move to 2.0 unstable.