This plugin seems incompatible with the latest WordPress version. I administer a network of three sites. After activating Gallery for all sites the fields in the dashboard failed to respond, i.e. I could no longer access the network admin or log out. Not being able to access admin from the dashboard meant I could not deactivate the plugin, so I had to remove all the files via my ftp access. This solved the problem.
That the plugin should freeze the backend seems to me not kosher, so I hope someone clears this one up. Thanks.