Collection letters Error

When sending the collection letters, the process ends with an error where it says "No Dunning Site Found, Looping through delinquent Billto Sites" "The contact information is missing for customer XX", but I check and the contact information and its responsibility are there .

The configuration is for several Business Units and only fails for the one with the most delinquent clients.

What will be failing?

Can you help me with this fusion function. I can't understand if it is because of the Business Unit, because the other two units execute the sending and receiving of letters well.