SOLVED Save - Oops Page Not Found (404)

[pbedford]

When trying to save ANY page I am getting redirected to admin/changedata.php with a 404 Error (Oops! Page not found!).

I can confirm existence of file admin/changedata.php. I can duplicate a page, I can create a new page. Just can't save edits. Used to be fine - as far as I am aware no configuration changes made to hosting server.

I have disabled all plugins and tried 3 different themes. Problem still there. Updated to lastest version Version 3.3.8. That didn't help either.

Any help greatly appreciated.