There was an error while trying to serialize parameter http://webservices.idibilling.com/OnlineBillConfiguration/1.0:Request. The InnerException message was 'Member GUIDKey in type IDIBilling.OnlineBillConfiguration.Client1.ValidateSecurityKeysReq cannot be serialized. This exception is usually caused by trying to use a null value where a null value is not allowed. The 'GUIDKey' member is set to its default value (usually null or zero). The member's EmitDefault setting is 'false', indicating that the member should not be serialized. However, the member's IsRequired setting is 'true', indicating that it must be serialized. This conflict cannot be resolved. Consider setting 'GUIDKey' to a non-default value. Alternatively, you can change the EmitDefaultValue property on the DataMemberAttribute attribute to true, or changing the IsRequired property to false.'. Please see InnerException for more details.