The USB stack in Rockbox is still incomplete. For now, use the original firmware on the H10 to transfer files to and from your device.
The UMS trick (which lets your H10 show up like a regular USB device) is recommended:
1) Connect your H10 to your PC using the data cable.
2) Push and hold SELECT as you turn on the power.
3) Continue to hold SELECT until the "Connected" screen appears.