Geometry Cleanup

Hi,

I was practicing geometry cleanup on one of the tutorial models (clip_repair.hm) for tutorial HM-2000. I successfully cleaned up most of the free edges except for one.It is a free edge that forms a closed loop  (missing surface). 

I used Geometry > Create > Surfaces > Spline/Filler, but it doesn't work.

Any ideas on why it doesnt work? 

Thanks,

<?xml version="1.0" encoding="UTF-8"?>