Since you are trying to make a straight line between 0 and 100 you could just leave it off for now, but does entering any other set of curve coordinates work? Can you test this with a different profile? Duplicate an existing working profile, rename it and drop in the curve coordinates like it is below here.
GRAY_HIGHLIGHT=6
GRAY_SHADOW=10
OVERLAP=0
GRAY_GAMMA=1
GRAY_CURVE="0;0 100;100"
I haven't upgraded to Yosemite yet, so I won't be able to get around to testing this until later next week.
Richard Boutwell