I've been working with WCF for quite a while, and every so often I run into this exception:

ArgumentException: The provided URI scheme 'https' is invalid; expected 'http'.Parameter name: via

The problem is obvious. You're trying to access a service under HTTPS, but it's being called with HTTP. Under most bindings you can solve this by adding somehting like this to the client binding configuration:

<binding name="MyBinding"> 
  <security mode="Transport"> 
    <transport clientCredentialType="None" /> 
    <message clientCredentialType="None"
             negotiateServiceCredential="false"
             establishSecurityContext="false" />
  </security> 
</binding>

When you use a (custom) ws2007FederationHttp binding, for instance when working with Windows Identity Foundation, the above won't work. In that case you need to look in the binding for the <httpTransport> element and replace it with <httpsTransport>.