No hay una correspondencia de restricción única que se dan claves para la tabla referenciada
It's because the name column on the bar table does not have the UNIQUE constraint.
So imagine you have 2 rows on the bar table that contain the name 'ams' and you insert a row on baz with 'ams' on bar_fk, which row on bar would it be referring since there are two rows matching?
Santino