I am using the automatic upgrade feature in 2.8.6. I have a dozen sites hosted on Rackspace CloudSites, about half of which the automatic upgrade works perfectly. For the other half, clicking the "Upgrade Automatically" link simply loads the page that says
"Downloading update from http://wordpress.org/wordpress-2.9.zip."
and nothing happens. I check the server and /wp-content/wordpress-2.9.zip is a 0B file. I don't think it is a server issue because some sites on the same server upgrade fine. I thought it was a plugin because deactivating WP Super Cache allowed the upgrade for one of the sites, but unfortunately, that fix didn't work for all. Thanks for any help with this.