If you get this message while trying to sync music to your Fuze, “WMP cannot access the file. The File might be in use, you might not have access to the computer where the file is stored, or your proxy settings might not be correct”, Black-Rectangle offered the simple solution that worked for me:
Take out your external card and format the internal memory.
I had just inserted a 32Gb card and it would not sync after a certain point. The formatting worked for me.
Thanks for all the help everyone and to Black Rectangle for the solution.