Thanks Jason, but what I meant was that I do not have a "WebAssist" folder in the "Shared" folder in which should be the "DocumentEncoding.js" file.
I have no trouble deleting the WinFileCache file and have done that a few times to remedy this issue. A previous poster wrote some code to put into the DocumentEncoding.js file but I do not seem to have it on my system.
I have been using WA extensions for years. I did just install the Design Extender after removing the other extensions that it replaces, if that helps with my diagnosis.
Is it a case of just getting that .js file and putting it where it needs to go? If so where can I get a copy of that file?