Why would south Carolina ask for a copy of my w2's before processing my return?

They want a copy of your actual W2 to match what your employer sent in.  Does the state withholding on your return match your W2 box 17?

Because them and the feds are both clamping down on fraud so if they cannot confirm the same W-2 info you entered with what the employer sent in then they ask for your paper copy.  Comply asap as directed.

it's also possible your employer never filed the W-2's or change something and didn't send you a corrected form.