Autentication method between TMG & Exchange 2013 for OWA

Hi,

I have tried to follow the blog article "Publishing Exchange Server 2013 using TMG" http://blogs.technet.com/b/exchange/archive/2012/11/21/publishing-exchange-server-2013-using-tmg.aspx

but I get an authentication error.

I'm using basic authentication in OWA and I have also defined in TMG but when I test the rule I get the following message:

Testing https://XXXwebmail.contoso.com:443/OWA/
Category: General error
Error details: The authentication delegation method defined in the rule does not match the authentication method selected for the published directory on the server hosting the site. Publishing rule authentication delegation method: Basic. Published server authentication methods: Forms-Based Authentication.
Action: You can change the authentication method on the published server or select "No delegation, but client may authenticate directly" in the Authentication Delegation tab of the publishing rule.

The listener uses HTML forms with widows active directory.

Any help would be appreciated.

Thanks

Joe