No idea there, there should be a number regardless of the issue.
Error 21 will of been caused because you messed the dashboard files up
ftp over the entire custom dash, there is no special setup to keep skins, but if there is something missing this may cause the skin to be reset, myself I have been using XBMC for years now with the skin MC360 with a older 360 clone skin used.21 - anywhere -
This error says that the machine was booted to display a error, basically someone told the machine to reboot (or launch a xbe) with this flag, and the error code just means its been rebooted by the flag
This occurs frequently when the xbox is unable to boot due to dashboard changes being made (ie Gcue true blue hasnt been resigned, parts of the stock dash are missing - incomplete FTP backups copied to a new HDD for example)
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