COULD MY SDHC CARD BE FULL?

I have 16GB card in my Fuze+…real capacity, 14.8GB…used space 13.9…free space 866MB, but the card has topped accepting music files with an average of about 120MB each.  Could my card be filled up and still showing this much free space?  My other drive (the Fuze+) is accepting files with no problem, of course.  Any help would be appreciated.