I am using Auto discover service Url for a specified e-mail address.
ExchangeService Service = new ExchangeService(ExchangeVersion.Exchange2010);
Service.Cr
Let me point out that if you are trying to access Office 365 then the web credentials really are of the form WebCredentials(strUsername, strPassword); with strUsername being the email address of the account you are trying to access.
I was getting this error and it turned out someone had changed the password on the account without informing me! What an odd error to get when it's just a bad password!