Napster has been messing with things recently. I've noticed I can no longer play my tracks in Windows Media Player, but I can use their own streaming player. If I double click on a track I've already downloaded, I get "Napster cannot play this track right now" or a DRM error. Further, you cannot restore the licenses by the recommended method of importing the tracks - Napster's software doesn't seem to recognize any of their own .wma files as even being there.
Napster limits you to three downloads per file per user account. After that, you will get a "No more downloads" message. It's a new restriction they've placed on their customers to limit any possible distribution of their files. You can theoretically renew the licenses month after month, but you can't redownload the same track more than three times.
I wrote to Napster about the DRM issue earlier today. It could be as simple as a problem with their DRM license server... or they are trying to further restrict what people can do with their files.