Here is the error that took me a few days of back-and-forth with an India programming team to figure out:
DateTime values that are greater than DateTime.MaxValue or smaller than DateTime.MinValue when converted to UTC cannot be serialized to JSON.
at System.Runtime.Serialization.Json.JsonWriterDelegator.WriteDateTime(DateTime value)
at System.Runtime.Serialization.XmlWriterDelegator.WriteDateTime(DateTime value, XmlDictionaryString name, XmlDictionaryString ns)
I found that I had an uninitialized date time property (meaning it was equal to DateTime.MinValue) in my data transfer object (DTO). If your WEST of GMT, this doesn't cause a problem; however, if your EAST of GMT, the DataContractJsonSerializer will puke.