Unable to create symbolic link

Sorry to trouble you on Christmas morning, but I'm having problems creating a symbolic link between two points on the SD card. I keep getting the told "Operation not permitted". Any ideas as to what I'm doing wrong?

Merry Christmas BTW!

root@Hydro:/mnt/sda1/arduino/test# pwd
/mnt/sda1/arduino/test
root@Hydro:/mnt/sda1/arduino/test# ls /mnt/sda1/arduino/reports
hydro-p-required.csv  hydro-p-sensor.csv    hydro-p.csv           startup.log           transcript.log
root@Hydro:/mnt/sda1/arduino/test# ln -s /mnt/sda1/arduino/reports reports
ln: reports: Operation not permitted
root@Hydro:/mnt/sda1/arduino/test# ln -s /mnt/sda1/arduino/reports .
ln: ./reports: Operation not permitted
root@Hydro:/mnt/sda1/arduino/test# ln -s /mnt/sda1/arduino/reports/ .
ln: ./reports: Operation not permitted
root@Hydro:/mnt/sda1/arduino/test# ln -s /mnt/sda1/arduino/reports/ reports
ln: reports: Operation not permitted