Off hand it might be a version compatibility issue. It says it is for 1.7.6 and likely you have a 1.8.0+ OpemRPG or Traispe.
Sadly there was a small change to the interface for plugins which means that file needs to be slightly altered to work with 1.8.0 although you could check out a 1.7.6 OpenRPG just to see the plugin working to see if it is what you want. Hmm. Did I make some notes on how to convert... it wasn't hard... I'd just rather not until you're sure its what you want.
Try this version maybe:http://www.assembla.com/spaces/openrpg/documents/bhj1nGIEir3RDKeJe5aVNr/download/bhj1nGIEir3RDKeJe5aVNr