inserting into multiple tables and autonumber problem

hiya it's again me

i have another problem now.in my database i have 2 tables that keeps the information of the new customers. one is :

Customer with the attributes:

Customer_No
Branch_Code
Resource
Future_News
Interested_Topic

Customer Contact Details with the attributes:

Customer_No
Customer_Name
Customer_Address
Customer_Postcode
Customer_Email


therefor Customer_No in Customer Contact details is a foreign key and the server is not allowing me to insert any data to customer contact details. But then again Customer_No has autonumber type that I still couldn't understand why is is giving errors.

Any idea about this???