the current hash is
{\\\"report_name\\\"=>\\\"Study/Control: ABIRATERONE ACETATE - 20151413355\\\", \\\"left_mue_start_date\\\"=>\\\"02-26-2015\\\",
I ran into a similar problem, though it was failing while parsing \"\". This is in regards to using Pact.IO. I mention it here since this is the highest ranked Google result while looking for the error I encountered. The solution in my case was to change the body of a POST in my C# application so that it wasn't using empty string, but a null string. Basically I added this before my HTTP call.
if (request.Method == HttpMethod.Post && request.Content!=null && request.Content.GetType()==typeof(StringContent) && request.Content.ReadAsStringAsync().Result == String.Empty)
request.Content = new StringContent(null);