1st togle the HOLD switch (on then off), then for a period of up to 60seconds hold the Menu+Center button(avoid slidding your finger on the wheel), this will reboot the iPod. Hopefully this fixes it! Don't be afraid to try it several times if doesnt work the first time, sometimes it is necessary to do it a few times.
Then see if Rockbox is still frozen like it was, do the same thing as above EXCEPT, as soon as the apple logo appears press Center+ Play/Pause to boot into disk mode (to get out of disk mode just reset it with menu+center). Then while it is in Disk Mode, connect it to your computer, do a restore with iTunes. Then re install the latest build of rockbox onto your player( you will need to put the bootlooder and the latest rockbox build on), I would recommend that you do this with the Rockbox Utility (
http://www.rockbox.org/twiki/bin/view/Main/RockboxUtility#Download).
Hopefully this fixes the problem, if it doesn't it very well could be a bug in Rockbox.