Why am I getting invalid XML as a response from EWS calls?

Just starting out with Exchange Web Services and getting a strange error right off the bat.

The Exception I get is "The response received from the service didn't contain valid XML." The Inner Exception is "DTD is prohibited in this XML document."

So any ide开发者_C百科as on what could cause that?

Turns out I was using the wrong url for the web services.