As I have written several times on this blog, I am using Napster 2 Go with my Creative Nomad Zen Micro. Unfortunately, the N2G compatible firmware from Creative is still in beta. Everyone in a while...not sure what the repro steps are...the Zen Micro would lose all the N2G music licenses. They've released new firmware (2.11.02) that is supposed to solve this problem.
However, while the new firmware will eliminate this from happening in the future, it doesn't help you with songs that have lost their license. So you have to delete them off the device and reload them. Simple enough to do w/ WMP10. However, the music you download from N2G has a set of license restrictions, including a limit for the number of times you can transfer it to a portable device per month. I think the limit is three. I've reset my device a few times experimenting with it, so about half my N2G songs had reached their limit. Major bummer.
However, I dropped a quick email to the folks at Napster and the next time I synced my device, suddenly all the songs had their transfer count reset. So I was able to resync even the songs that didn't work before. I had figured I wouldn't get those songs back until next month, so I decided to download some other stuff to tide me over. Having the older songs transfer was a very pleasant surprise.
Bravo Napster Support!