[Plugin: WordPress Automatic upgrade] Blank screen after DB backup

I’m trying to use this plugin without success. After I click “Next” to go to the DB backup page, I see the WordPress toolbar but underneath that is a blank white page. So I backed up the database and skipped to the next step manually. When I instructed the plugin to download the latest files from WP and clicked “Next”, I got the same blank white screen. Nothing happens at all. Eventually I clicked on the “upgrade automatically” link in the toolbar, and it asks me to “clean up”. I do that, start over again – and the same thing happens.

I’m using Safari on a Mac.