Remember the Tomcat woes I was experiencing on Monday? Well, I think I've figured it out! It wasn't too hard, all I had to do was read the error message ...
... and go looking. Sure 'nough, this class is not there, nor are any of the other classes for the admin webapp! So I've logged the bug and now I wait. Maybe this is intentional, but I doubt it.
Later: The workaround I'm using is that there's a milestone build from October 14th that has the admin app intact and no errors on startup.