Hey futsec,
When you plug in the duck to a computer it needs to install drivers for the HID, which is the Duck.
so,
You should try the DELAY command to the top of your script, and else where like so:
DELAY 3000
REM --> Delete Log.txt and exit
DELAY 150
STRING del Log.txt
ENTER
DELAY 150
STRING exit
ENTER
You need to use the delay command in between some commands so the computer has enough time to process the information before you spam it with key strokes again.