I was having problems upgrading to WordPress 2.7.1 with the Automatic Upgrade plugin, so I did a bit of research and automatic upgrades are now built in to WordPress. How did I fix it? I deactivated the Automatic Upgrade plug-in and now upgrading automatically works fine with no plug-in necessary. So deactivate your Automatic Upgrade plugin, by going to plugins section and WordPress will automatically upgrade to WordPress 2.7.1 for you, no plugin needed.
Giddy up, easy as pie..