Its software allows video creators to embed instructions for the player to show several kinds of advertising in videos, including pre-roll video ads, text ticker ads that run along the bottom of the image, and small clips displayed in the corner of a video.
So, if you're trying to use Napster to Go with the iRiver H10, and you're seeing the same problem, check out this thread and follow the second set of instructions (there are two on the page) to reformat your player, then re-transfer your NTG files and try again.