Hi Joe,
Are you accessing reports developed using CR 2013 designer?
SAP Crystal Reports RESTful web services can only work with reports created with SAP Crystal Reports for Enterprise when using the RESTful web services.
the same information is documentated in the pdf for SAP Crystal Reports RESTful web services available at
http://help.sap.com/businessobject/product_guides/boexir4/en/xi4sp6_cr_restful_ws_en.pdf
Execute the same urlfor reports designed through CR4E designer and you will be able to get the response.
I have tested it at my end and it works.
Thanks,
Prithvi