You found a bug in ISBoxer, that's all. Based on your error message I've fixed the error and updated the download.

It seems to be from having a Step with no Actions in it -- ISBoxer 33 automatically adds a Step to any new Mapped Key, and Zanthor's guide was made for ISBoxer 32 which did not. In fact, if you watch the video in my post directly above yours, you can see that I pretty much built the key maps from this guide into the Quick Setup Wizard, so that might be of interest to you. Anyway, the solution (other than re-downloading or waiting for a pushed ISBoxer update) is to find that Mapped Key (the Send Next Click one from the guide), and either add a Popup Text Action to the Step (e.g. say something about gogo send next click) or delete Step 1 from it (click it and hit Del, or right click it and select Delete, either should work).