celinedrules think about whats happening here, of course it will give you error 21, your not running a debug bios! the various software exploits relay on your xbox booting FIRST to an exploitable dash (this file is called xboxdash.xbe) so you cannot remove this file from the C drive else your xbox wont boot.
Read through the hydras tut, it states that you only need to copy xshell.xbe, the only thing youd nee to do different is to use a BFM equiv bios, i 'think' yoshihiros new bfm debug bios would work, from ym understanding ti will boot the xdk launcher from C (xkshell.xbe) and if thats not present it will boot C:\evoxdash.xbe then C:\xboxdash.xbe.
Regards, Guy