I don't have Poser Pro, so I can't test....

I think, though, that PP uses a new version of TKinter which handles
the "initialfile" option differently.   Try eliminating the initialfiles bit. 

In other words,

Change line 252 in the PY file from

        fn=tkFileDialog.askopenfilename(initialfile=MyPath, filetypes=[("BVH files", "*.BVH *.bvh")] )

to

        fn=tkFileDialog.askopenfilename(filetypes=[("BVH files", "*.BVH *.bvh")] )

I've italicized the part to remove in the original line.

My python page
My ShareCG freebies