If you've rooted your Android device in order to get rid of certain pre-installed apps, or to install a custom ROM, take note that it'd be blocked from the Android Market's movie rental service.
This tidbit of info comes from the Google Android Market support forum itself:
I see "Failed to fetch license for [movie title] (error 49)” when I try to download.
You'll receive this "Error 49" message if you attempt to play a movie on a rooted device. Rooted devices are currently unsupported due to requirements related to copyright protection.