Thanks Gary, that worked. I'm still not sure what caused this grade to be "grayed out" in the first place for this particular student. I have tried to duplicate this condition, but have not been able to do so.
I typically use the assignment submission page to grade. If a student resubmits work, or hands it in late, I then use the Update function when I look at the list of submitted assignments if I have already given them a grade. When I do this for this student, the Update page is grayed out as well.
Do I have cause for concern or is this normal?