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Could you type out the full error messages? -1 usually means you have installed the bootloader but not the build, i.e. you haven't correctly unzipped rockbox.zip to the disk.
This is also the one active when you connect your player to USB when it's turned off. So you would need to connect your player this way and just follow the instructions on how to "upgrade" your firmware - as you can find them on Cowon's site: www.cowonglobal.com - support, firmware upgrade (you might need to create the mentioned FIRMWARE directory if it doesn't exist on your player currently and maybe clear the .rockbox directory afterwards).
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