Answer
Work through this checklist: confirm the physical printer is powered on and that you can print to it directly from the Print Agent host machine, logged in as the same Windows user account the Print Agent service itself runs as (checkable via the service's Properties > Log On tab in Windows Services); confirm the correct printer and its drivers are actually installed on that Print Agent host; confirm the same IFS Logical Printer isn't configured on two different Print Agents at once (a Logical Printer should only exist in one Print Agent's configuration); and check for any intermittent network connectivity issues between the Print Agent host and the physical printer, since a brief network drop at print time can produce exactly this error.