The purpose of this study is to assess the efficacy of esomeprazole (D961H) 20 mg versus placebo once daily for up to 24 weeks of treatment involving patients with a history of gastric and/or duodenal ulcers receiving daily nonsteroidal anti-inflammatory drug (NSAID) therapy by evaluating presence or absence of gastric and/or duodenal ulcers throughout the treatment period (24 weeks) in terms of efficacy on prevention of gastric and/or duodenal ulcers