What does it say at the top of that form? "Do not complete this schedule if all of your California gains (losses) are the same as your federal gains (losses)."
Did someone loose the corresponding state K-1? If you know the state is different are you not able to make an entry is state, if different?
Give more information and you may get more help, e.g. What flavor is that K-1 that has lines 4(a) and 4(c). Volunteers here are smart, but we are a bit lazy and hate looking up things those that post should include.
I don't know why you would get that diagnostic. CA Sch D is not a requirement for e-filing; so, I have NO clue why your efiling wouldn't go thru without the CA Sch D. It doesn't make sense to me from the angle of CA tax e-file processing.
Entering -1 for the state amount would trigger Sch D for CA - yes - but if your client had CA source income or CA tax, the CA tax computation would be off/wrong. Basically CA NR tax is computed based on the percentage of CA source income applied to the CA tax (Line 31 on 540NR). By entering -1, you would change the computation of Line 31.
However, if your client didn't have significant CA tax, who cares, right?
If the accuracy for your client's CA tax is important, consider changing the state number by $1 instead of entering -1.