That generally means that no receipt template is defined for that transaction type, or that no receipt format is selected for the register.
Look at register properties for that register and check the Receipt format that is assigned for Printer 1. Also check printer 2 just to see if anything is set up there.
Go to the properties for any Receipt Formats you found, and make sure that the transaction type you selected has a template defined. Sometimes templates are removed from a format on purpose - for instance some people like to have one format for transactions and a different one for Quotes or Work Orders.
If everything is in place, it's possible that the receipt format was not assigned until after the transaction was processed...