I’ve been trying to work on fixing the Press This functionality for months now to no avail. A lot of solutions have involved copying the code from the site, adjusting the javascript and adding in the URL of your site.
I have just fixed the problem, for me at least, using the steps from the following site. Thanks!
How to fix “Press This” 404 errors
via How to fix “Press This” 404 errors | Blog Mum | WordPress made easy.