Additional Study Information: The purpose of this research is to find out whether an experimental drug called maribivar is safe, and whether it is more effective than the medications we usually use to treat resistant CMV infections. Half of the people who choose to be part of this research study will be given maribivar, and half will be treated according to their physicians usual practice. The groups will be assigned by chance, like by a toss of a coin.The majority of people at some time in their life become infected with CMV but do not know they have it. Even with use of medicines to prevent CMV, a CMV infection or disease can still occur. Cytomegalovirus (CMV) is a viral infection and can happen in transplant patients. In patients with certain conditions such as transplant or weak defense system (a system that protects you from disease), CMV can become active and they can have symptoms of the disease. When CMV is active, it can be found in the blood. CMV infection can lead to disease involving different organs.