Instructions
Download the movie you are trying to watch instead of attempting to stream it. You can choose between the two options when you purchase the video. Depending on the stability of your Internet connection, trying to stream while watching may cause errors with your Zune playback.
Delete the video by navigating to the "Memory" node under "System Settings," selecting "Hard Drive" and choosing "Videos." After the video has been completely removed from the system, try re-downloading to see if your issue is resolved.
Check other videos to see if a similar error occurs. If so, the problem may be with your system and not with the video you are trying to watch.
Clear your Xbox 360 system cache. Open the "System Settings" menu and navigate to "Memory." Highlight any storage device, hit the "Y" button and select "Clear System Cache." This will reset the temporary memory on your storage unit (your save files will not be harmed).
Test your Internet connection in other parts of your home. If other computers are experiencing connection issues, you may need to speak with your Internet service provider.