Neil, I have the same setup as you (pretty much) and am familiar with the headaches.
1. Boot into Rockbox in whatever way you can (CF, RAM or ROM)
2. Plug in your USB be cable and enter Rockbox Diskmode.
3. Rename you .rockbox folder (example old.rockbox) and unzip a fresh copy of .rockbox.
4. Unmount and unplug you player from the computer.
5. RoLo into the rockbox image on you CF Card. (you should be prompted to do this)
6. Clear all of your settings. (may not be necessary but better to be safe)
7. Shut Down
9. Engage the hold switch
9. Reboot
10. In the bootloader set "boot from disk" as default.
11. Boot from disk!
You should now be OK. Let me know how it goes.