http://www.someorganization.com/arcgis/rest/services
Did you verify that the REST endpoint is accessible?
Example:http://www.someorganization.com/arcgis/rest/services
If you have a way of testing this from outside your network, it is better because you will see what users outside your network will see. A USB cellular modem works well or an iphone or android phone's browser. Or ask a friend who is outside your network to check the REST endpoint.
Paul Lohr