Hi again,
I called to my very friendly Iriver Support Tech who fixed me right up. She said that the s10 required a fast USB drive (which corresponds to MauwzerDAP's solution) so I should try using the USB port at the back of the computer rather than the front. Worked a charm, and I'm so relieved!
Other advice given:
- Don't use the Windows drag-and-drop method to add music, as it can disrupt the file organisation.
- Music from free sites can cause a problem, and some paid music can only be transferred a certain number of times.
Use the Iriver program, and the transfer button in particular, to add music.
yay iriver!