Python 2.5 with xem3001 :device could not be opened

I installed python 2.5 , numpy-1.2.1 and Frontpanel 3.0.11. Then running the sample example DES gives me the following error message:

------ DES Encrypt/Decrypt Tester in Python ------
A device could not be opened. Is one connected?
Usage: DESTester [d|e] key infile outfile
[d|e] - d to decrypt the input file. e to encrypt it.
key - 64-bit hexadecimal string used for the key.
infile - an input file to encrypt/decrypt.
outfile - destination output file.
Traceback (most recent call last):
File “C:\Program Files\Opal Kelly\FrontPanel\Samples\DES\”, line 125, in
strkey = sys.argv[2]
IndexError: list index out of range

I’m newbie to python. Besides installing the above software, is there any other settings I need to check/change ?