I suspect you’re missing a myo component. In order to use input mapping you need to have a Myo Component attached to something that is placed in the map. Typically the easiest place to add it is to your pawn/character. After you’ve done that your input mapping events will work. You should also attach the interface so that the plugin won’t warn you about lack of interface bind (used for non-IM blueprint events)
Here is a quick video on how to add myo support to the rolling template in under 60 seconds.
Edit:
Thalmic Labs have posted a page outlining the steps in a simple format, highly recommended for concise instructions:
http://developerblog.myo.com/myo-unleashed-gesture-control-in-the-unreal-engine/