I get this error: "You attempted to reach a non-existent page. Please check the URL and try again."
I contacted support a few days ago and have not had a reply yet.
Have you tried another browser, or tried updating your current browser if it's a few revisions old?
Also, another common fix that seem to help in many cases is simply rebooting your machine, and logging in from a fresh page (adwords.google.com) rather than a bookmarked page.
Clearing your cache and cookies may help as well.
And of course, writing AdWords support with this sort of issue is a pretty good idea, especially in you've been having the same problem for a number of days.
I hope one of these ideas takes care of it.
AWA
I think its invariably because you will have some javascript file cached on your local machine. Google then does an update, but reuses the same javasciript file names. As a result your cached javascript file no longer is the proper working one that you need. As a result you see this kind of behaviour, and are told to clean your cache.
If google, applied some kind of versioning system to their javascripts, ( or at least change the names) they could avoid this kind ofproblem.
1 way could be to maintain a directory of version number, then script name.
e.g.
/v22/somescript.js
so when you do an update the new script would be referenced by
/v23/somescript.js