urllib.open problem

[Astan Chee]

Hi Guys,
    I have a python script which runs perfectly on my machine.
    However a machine that I tested it on gives the following error 
message:

    Traceback (most recent call last):
      File "whip.py", line 616, in OnRebootRunning
      File "whip.py", line 626, in RebootCustom
      File "urllib.pyc", line 77, in urlopen
      File "urllib.pyc", line 170, in open
    TypeError: cannot concatenate 'str' and 'NoneType' objects

    The code snipplet where this error
    happens is
    f = urllib.urlopen("http://www.hotmail.com/)
    notes= f.readlines()

Does anyone know what causes this error? Im perplexed because it works 
on some machines and it doesnt work on other computers although they all 
have the same spec.
    Thanks for the help
    Cheers
    Stan