What is the issues ?

[roshan991]

swswd

[majd0]

I guess this issue when you tried to add a new Customer to DB and redirect to Index Page.
So the Model can't reference the MembershipType.
Make sure the data entered into the Customer table are added successfully (all columns).

If the MembershipTypeId column is Null then you have another issue.
See the column's name and look if they differ from the actual model properties.