I suppose that your problem might be in your client certificate. Setting clientCredentialType="Certificate" you tell WCF, that client must specify a certificate trusted by the server. As I've understood, you have only server-side generated certificate. Try to set
<transport clientCredentialType="None" />
This will allow you to send messages without requiring certificate trusted by the server. Or you can try to generate certificate on client side and put it into Trusted folder on your server. Maybe this state will help you http://msdn.microsoft.com/en-us/library/ms731074.aspx