Hi,
At a terminal window as user knoppix try the following commands to save a previously created file called newfile1.txt:

knoppix@ttyp1[knoppix]$ su
root@ttyp1[knoppix]# mkdir /mnt/usbstore
root@ttyp1[knoppix]# mount -o uid=knoppix -t vfat /dev/sda1 /mnt/usbstore
root@ttyp1[knoppix]# exit
exit
knoppix@ttyp1[knoppix]$ cp newfile1.txt /mnt/usbstore/newfile1.txt
knoppix@ttyp1[knoppix]$

If this is successful then try the same with a shell script file.
Regards,
Mark