Cleared Tiki Cache -no dice.
I'm using Milkyway without mods except for some color value changes in the CSS -done ages ago.
Under PHP Error Reporting Level I chose "Report all PHP errors" and "Visible to admnins only". I went to a page, clicked edit and got the blank screen again -no error reporting is visible on that blank screen. I went back to the home page url and no errors were visible (I am logged in as admin).
Just for fun I did a "view source" on one of the blank pages and all that shows up is a single digit: 1