When I change a node title and hit save, I get 'page not found'
When you change the title of a node when URL auto-alias is turned on, you will need to fix your links to that node or do the options below. You are getting the page not found error, because it's trying to go back to the view version of the node that now has a different URL. You have the following options:

Install redirect. Then set up a redirect to the old URL. If you install this first, it will automatically track the changes of the URL moving forward. 

Alternatively, you can go to the node and uncheck the auto-alias option and hand-assign the URL back to what it was before you changed the title. I recommend the redirect module though.