Si nos aparece este error especificado en el título podemos solucionarlo aumentando el valor de MaxItemsInObjectGraph del siguiente modo:
Error

Maximum number of items that can be serialized or deserialized in an object graph is '65536'. Change the object graph or increase the MaxItemsInObjectGraph quota.

Solution: Edit app.config

<configuration>
   [...]
   <system.serviceModel>
      [...]
      <client>
         <endpoint address="URL"
                   [...] 
                   name="myName" 
                   behaviorConfiguration="customQuotaBehavior" />
      </client>
      <behaviors>
         <endpointBehaviors>
            <behavior name="myName">
               <dataContractSerializer maxItemsInObjectGraph="409600"/>
            </behavior>
         </endpointBehaviors>
      </behaviors>
   </system.serviceModel>
</configuration>