First off, just so you know adb only works from a PC side. adb allows you to access your phone via command prompt. You can access other commands you can't through terminal, like push a file from your PC to a specific spot on the phone, and pull a file from the phone to your PC. A pretty nice writeup [ HOW TO ] ADB AND WHY I LOVE ADB commands <3 . Not that any of this matters right now, but that is why adb shell in terminal emulator comes up with errors.
Maybe busybox doesn't have the right permissions.
Code:
su
mountsys
chmod 755 /system/xbin/busybox
Then try typing "droidboot" or whatever script you are trying to run.