Sorry if this is old news, but if anybody is having problems with mx-editor for mx-800/mx-700, I got my to work.

First, after installing vista I was able to install the mx-editor without issue.
However, I couldn't live update. It would fail with "fail to install patch" or something.

I noticed mx-editor and subdirectories were all read-only and I couldn't change it.

I turned off the user access control in the control panel and rebooted.

I can now update.