Dunning Erroring Suddenly for a BU

We've been running send dunning for several years, suddenly this month a whole BU has error'd an we're unsure why. We understand that a customer may not be configured correctly, but that normally doesn't error the whole job. We've been able to run all other BUs but this one, which is odd and last month this program worked for this BU that now has an error even though the customers are the same. I'm curious if anyone has experienced this.

We get this error but it doesn't make sense to us since it's been working fine previously for the same BU and customers.