I am getting this same error when trying to sync songs to my Sansa Fuze. A block of songs did not sync. I got the error Object reference not set to an instance of an object. These songs all play just fine in MusicBee on my computer, but they could not be copied to my Fuze. Interestingly, they were all in a block grouped together alphabetically (artists Daughtry, Dave Matthews, David Bowie, David Cook, Dazz Band, Dead or Alive, and Depeche Mode).