Unfortunately, that didn't resolve the issue. I even went through that process twice (testing at each point) and still same error.
I turned on debug and here's the full error that is displayed:
Call to a member function update() on null
I've taken a look at that editor.php file code and I'm not at all sure what the problem is - without completely re-tracing the entire code.
Just wondering if that helps at all with trying to identify this. Wondering if any certain type of extension might be causing a conflict.
(let me know if seeing more from the Call stack would be helpful to track this)
NOTE: There are no JS errors displayed on the page at this point.