When adding a customer account to OTRS 3.0.11, you may encounter the "user already exists!" message but the customer account isn't visible in the Customer Management page. The problem is that the page doesn't indicate that you may have more than one page of customer accounts and there is no way to see more pages (i.e. no "Next" or "1, 2, 3 ..." links). The workaround is to restrict the search, e.g. if you are looking for "johnsmith", enter "john" or "smith" in the Search field.