I just ran into this problem after installing the iFlash Quad into my iPod 5.5g. I was confused what "OF" meant. I figured out it means rebooting your iPod and quickly locking the lock switch so it boots into the iPod's Original Firmware. When it's done rebooting iTunes will load, if you have it installed. You can immediately quit iTunes. Double click the iPod and find your music folder. Now transfer over your music using drag-and-drop. Once you're done, unlock the lock switch and once again reboot your iPod. It'll now load into Rockbox and your newly transferred music will play without skipping.