Currently MapViwer saves the registration information in the computer's registry. You must be logged in to the computer with Administrator rights to save information to the registry.
If you are not the Administrator, you can resolve this issue by right clicking over the MapViewer shortcut or application and clicking Run as administrator. That will open MapViewer in administrator mode. Select Skip registering and click Finish.
If you cannot save this information to the registry, then the program will prompt you to register the software each time you open it.