I've just installed MT 4.2, and am trying to start changing my templates to take advantage of the community features. First stop, sign-in. I followed the instructions on this page - http://www.movabletype.org/documentation/designer/creating-a-sign-in-link-on-your-blog.html and updated my javascript file per this page - http://www.movabletype.org/documentation/designer/site-javascript.html. But when I add the sign-in link I'm getting errors on the page:
commenter_name is undefined mtUpdatesigninWidget is undefined.
The signin page says that mtUpdatesigninwidget is in the javascript file, but I don't see anything there.
What am I missing? Where is mtUpdateSigninWidget??
Reported on Movable Type 4.2

When in doubt, go to System Overview > Global templates and search for it. That function is found in the global "Sign In" template module.
If it and commenter_name aren't defined, it means that those routines aren't being loaded. Check that you are loading your blog's javascript (mt.js) and that somewhere along the line the Sign In module is being loaded before either of those functions are called.
My guess is that you one of your edits removed the call to those templates/scripts.