I then installed the older version to make sure I did not mess up Chicago and Las Vegas and they were still good
You shouldn't do that, because you will need the new version of the software to activate anything in the future ( change of hardware, windows reinstall, etc ) so, the right thing to do is, instead, fixing the problem in your system that is preveting the new Addon Manager to work.
You don't say anything about your OS version. The Addon Manager requires an updated .NET library so, if you still use Windows 7, you must manually search for it, since Microsoft is not keeping it updated automatically anymore.