Systemic sclerosis is a widespread connective tissue disease that involves changes in the skin, blood vessels, muscles and internal organs. This research study is testing an experimental drug called treprostinil diethanolamine for the treatment of digital ulcers caused by systemic sclerosis of scleroderma. The purpose of the study is to determine if treprostinil diethanolamine is effective at healing digital ulcers compared to placebo.