xboxdash.xbe is the first xbe that the bios starts.
The bios expects a signed application.
Due to the softmod exploit, the execution is transferred to the nkpatcher xbe that alters the bios in ram and starts another xbe which you might find in the E:\dash folder or something equivalent.
So, you changed the xboxdash.xbe to an unsigned application which the bios refuses to run.
Ftp is a dashboard functionallity. As long as you don't have a dashboard like Xbmc or unleashx, you can't ftp to your xbox.
You will need another way to access the contents of the xbox harddisk.
You could temporary install a modchip in your xbox and use the Slayers rescue disk as dashboard.
You could connect the disk to your pc and use xbplorer360 and xboxhdm to alter it's contents.
You will need to unlock the disk and disable it's security before you can access it's contents. To do this, you will need the xbox eeprom.bin file (A copy of the xbox eeprom chip contents.)
You can build an eeprom reader to get that file or you can temporary install a modchip.http://forums.afterdawn.com/thread_view.cfm/357863
describes the eeprom reader.
Remodding the disk with a game exploit as ldotsfan suggests might work as well.