What does "address is not assigned to me" mean?

If a registered user tries to place an order when the shipping and billing address entered does not match with the information that is already saved in the account then the customer could receive an error stating that the address is not assigned to them.

For customers who need to update their account information please log into "My Account" first and then try placing the order. The customer can also try deleting the cookies and temporary files in their browser and then they can place the order.