"My code attempts to access a file share using the account of the user who is running it, who has been denied access to it. When this process fails the I attempt to impersonate the Administrator account"
Sounds like things are working as they should - you need the administrator password too.
This might help you to do it right (You will still need the password):
A small C# Class for impersonating a User[
^]
Best regards
Espen Harlinn