There have been reports of certain H10 models not working with Rockbox. It sounds like your model may be one that is affected by this problem. Don't worry though, your H10 isn't bricked, it just means Rockbox won't work on it yet.
If you want to go back to the iriver firmware, all that you have to do is connect your H10 to your computer in UMS mode, then copy the original H10.mi4 file back to the System directory.