reset while "Refreshing your media"

[cube]

Hi i have a new 8G clip+. At first i loaded it with some 800MB of music and it worked perfectly. Yesterday i tried filling it more (but still i left about 700MB), but it always resets at about 80% of “Refreshing your media”. I have a feeling that it is caused by some file that clip can’t handle, but i don’t know which one that would be and i don’t feel like manually removing and adding back every track to find out if it causes the trouble. Any ideas?