The problem is that you're using Slayers on a softmodded Xbox, even though the instructions warn you not to!
Here's a better process:
Build your xboxhdm disk using the stock C from Slayers / AID, and Kingroach NDURE 3.1. Put the stock C in linux/C, and the Kingroach 3.1 files in linux/ndure (the Kingroach C and E directories and the ndure script should be immediately below this i.e. linux/ndure/C/ and linux/ndure/E/.) Put eeprom.bin in /linux/eeprom/
Run xboxhdm, select option 1 - boot VGA Console, then type xboxhd, then select option 2 - Rebuild C partition on existing Xbox drive. Once that has finished exit, then type xbrowser, run the ndure script, then select option 1. Exit the ndure script. Reboot the PC, select option 4 and type lockhd -a to lock the disk
Now put the disk in your Xbox, and it will boot the softmod. FTP XBPartitioner 1.1 to the E partition (put it in E:\Apps\). Run XBPartitioner 1.1, and use it to format your F/G partitions.
FTP the stock C (from Slayers) to the shadow C (which will be empty). Your softmod is now complete and your disk is formatted and ready to go.
To change the dash you have to copy the dash you want into E:\dash\ and rename it default.xbe. If you want XBMC as a dash you can install it in E:\Apps\, and put the shortcut and its cfg file in E:\dash\, renamed default.xbe and default.cfg.