Grasshopper for Mac using Rhino WIP doesn't open .gh files?

Hello,

My Macbook is bootcamped and I have Rhino installed on my Mac side. I needed to learn Grasshopper for a project so I downloaded it for Mac using Rhino WIP (so that I didn't have to buy Rhino again for my Windows side). It seems to be working fine apart from the fact that no grasshopper files open once I have saved them on my laptop, or am for example trying to open a grasshopper file that someone has sent me.  I get an error message saying: "The document could not be opened. RhinoWIP cannot open files in the “Grasshopper Binary” format." Any ideas on how to fix this?

Any help is appreciated. Thanks - Margarida