Also, if you get a refusal of an offer with a red X, and the "Negotiate" link goes away on the "Draft Results" page, be sure to keep the email with his refusal. There's a link with the email that can bring you to the negotiation page. You can then continue to negotiate.
I was able to sign a first rounder who refused my initial offer with the red X, and I was able to sign him by resubmitting the exact same offer.