Integration with between Dynamics NAV 2016 and CRM

Hi All,
I'm integrating CRM and NAV 2016. I have managed to integrated custom fields but having trouble with Option fields. I created new option field in NAV with options: Blank,Individual,Member Organisation,Non-Member Organisation and in CRM field is new_customer_type with pickup list Individual,Member Organisation,Non-Member Organisation. I have added field in Integration Field Mapping with ExternalName = new_customer_type and EnternalType = Pickuplist. Every time, sync, Customer Type is set to -1, it ignores CRM Data. Can anyone help me!

With Regards
Sud