python win32com Lotus Notes Dispatch error

I'm trying to use python to access Lotus Notes using the win32com module

import win32com
from win32com.client import Dispatch
notesSession = Dispatch('Lotus.NotesSession')

However, I get the following error message:

pywintypes.com_error: (-2147467259, 'Unspecified error', None, None)

If I try a different application, eg. 'Excel.Application', I don't get the error.

Is there anything additional I need to make Lotus Notes accessible to python?

Thanks Toby