I'm having the same problem. MANY of my apps didn't work after upgrading from 8.0 to 8.1. So far all but this required the app to be un-installed and re-installed. And if the "answer" is to do a NEW "clean" update of 8.1 (and have to spend HOURS re-installing the Universe on my laptop) I'm going to ACCURATLY interpret that as there is no real GOOD way to do this, it’s our fault, the 8.1 upgrade is a obviously a failure. You can try this (no guarantees though) if it’s REALLY vital and/or you have lots of free time and it MIGHT work.