This can be a result of wrong code or different pieces of code clashing and not working well together especially when you add your own scripts. In your case when I removed the analytics script you inserted in Settings / Global javascript I was able to edit / add new pages after that. So you can try to re-acquire (in case its wrong) and re-insert this script on individual pages until you find the the code that is clashing with this one, but its not going to be easy since you have quite a few 3rd party tools on your site.
Jim Sympathy, Fluid Apricot