You need to reset the path to point at the folder containing the CoH application.
I'm having the same issue of pressing the play button, it saying "Launching Score" then changing back to Ready to Play.
I have already reset the path. The current path is to the "coh" folder downloaded via the torrent magnet link (in which "cityofheroes.exe" resides with all of the other game files). But I am still receiving the same issue.
In case it helps: right now I have a "CoH" folder in which both Island Rum and the above mentioned "coh" folder reside. If I need to change anything at that level, please let me know.