I had the same problem, with a ZERO getting prefilled into the disallowed wash sale amount and then Turbo Tax would not allow me to edit the amount.
How I fixed it:
If you right click on the field in the form which has the pre-filled ZERO in it, the pop-up menu appears, select "OVERRIDE", then type in the disallowed wash sale amount.
Not exactly intuitive-- come on Turbo Tax you can do better.
Hope that helps!
