If you have been experiencing this, it is due to a missing file in the iPod_Control/Device folder of the ipod. Got the solution from this post here Ipod Nano 5G with linux
I'll just list the steps here
1. Get the firewire serial id, look for a sixteen digit number in the output.
sudo lsusb -v | grep -i Serial
2. Add/Change the line 'FirewireGuid: ...' to 'FirewireGuid: 0x<firewire serial id obtained above>'
3. Get a HashInfo file from here by entering the firewire serial id (without the 0x) in the box and the click generate. Move the HashInfo file to you iPod_Control/Device folder
The error should go away afterwards