Complete the other state return first. You must have filed a return with another state in order to claim this credit.
The credit is available to a South Carolina resident or a part-year resident if state income taxes are paid to South Carolina and another state on the same income. The credit is computed only on income that is required to be taxed in both states.
You may claim the credit on your South Carolina return only if you actually filed a return with the other state and had a tax liability to the other state. Tax liability does not refer to the tax withheld from your pay, but rather to the tax computed on the other state's return (the amount the other state did not refund to you).