Hi,
I have installed demo data from dozens of themes before, but I’ve never seen this error.
I selected the XML file and uploaded it, then selected my admin username and checked the box to download attachments. WordPress then went to the theme’s 404 page. I tried reimporting the dummy data again and got a list of import failures (and some successes), and got duplicates of all the menu items, so that came in twice.
I wiped my server and tried installing WordPress fresh again. I tried importing the demo data again and got the same 404 error. How can I import the dummy data correctly?