You're trying to use a version of the hack that was created before the 2.3 firmware update. If your DX has been updated (home > menu > settings then look at the bottom right corner of the screen) you need to use the new version of the hack. See the link in my sig.
If your Kindle has not been update yet, you should do a
manual update *before* installing the new hack (Kindles will not update with 3rd part hacks installed).