Error related to data contract

{"Type 'GeneralMills.ConsumerServices.ContactUs.Protocol.DataDefinitions.ContactDataRequest' with data contract name 'ContactDataRequest:http://schemas.datacontract.org/2004/07/GeneralMills.ConsumerServices.ContactUs.Protocol.DataDefinitions' is not expected. Consider using a DataContractResolver if you are using DataContractSerializer or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to the serializer."}


Can any one help me to resolve this error? What would be the actual problem. My datacontract class is ContactDataRequest