re: the next / back buttons and commenting out the die() statement … this is only necessary for non logged in users. For logged in users, it works fine, at least for me (found out the hard way). That’s probably not using the right wp ajax stuff. Tested on 2.1.3.
After upgrading to 2.1.7, instead of a “Request has failed” on back/next, I get a -1 displayed (non-logged in users only). So I reverted, commented out the die() statement (which I am not comfortable doing for security reasons). But buttons work now. There was also a missing js file in 2.1.7, in my download, jquery-qtip.js.