A Study in Patients With Erosive Esophagitis to Investigate Safety, Tolerability, and Healing Rates After 4 Weeks Treatment of X842 or Lansoprazole and Symptom Pattern During Subsequent 4 Weeks Treatment With Lansoprazole

This study will be conducted in patients with erosive esophagitis due to gastro-esophageal reflux disease (GERD) Los Angeles (LA) grades C or D, and in patients with at least partial symptom response but still endoscopically unhealed (LA grades A or B) after 8 weeks history of standard treatment healing course with PPI, designed to support dose selection for Phase 3 and to investigate safety, tolerability, and healing rates after 4 weeks treatment of X842 or Lansoprazole, and symptom pattern during subsequent 4 weeks treatment with Lansoprazole.