eMailing Dunning error

We are on R12 and currently print dunning. We want to send it thru email and I did test it sometime back and it worked fine. Today before putting the setups in production I again tested after making the required changes and I got the following error. There is a host defined but the error says that host needs to defined. The setup for email I did was in 'Setup Checklist'--> Setup Correspondense --> Oracle XML Publisher --> eMail Host, From address and then went to Collection Methods Setup --> Create Dunning Plan and changed 'Method' to email in step 3.