That means that you've got customer entries that don't match your address_book table entries in your database.
This usually happens when doing an incomplete import of customer data from an external source but not taking into account how the various database tables work together.

It also suggests that you're using a very old version of Zen Cart ... because the line numbers you mention don't correspond with related code in current versions of Zen Cart.

Either that or you're using a contribution which has modified core files ... and is maybe designed for a different version of Zen Cart.