"Unknown Error" every time adding new track, and playlists not syncing

[kfilks28]

Every time I add a new song to a playlst, I get the error "Unknown Error" and I hit continue and it just dissappears, but it happens repeatedly and I'm not really sure what the error means. The songs then aren't downloading to my phone.

Additionally, I have many playlists downloaded, however some remain at like 97% downloaded, and newly added songs don't download. 

I'm running Jellybean on the Galaxy S3, have plenty of available space, have my computer and phone on the same wifi ....and deletion and re-install didn't help. Any advice on fixing this?