This KB article describes a possible reason of a failing inline verification in case the printer is connected via USB.
The Proof for Contract Approval task fails with the following error message:
"Error message: clEPSON_PORT::Close: Printer not readyJob has errors!"
Above error is a generic message used for many inline (ILS20 / ILS30: Epson SpectroProofer) verification issues. But if the printer is connected via USB then be sure that the Windows driver is installed.
The driver is required for the communication with the SpectroProofer (only in case when the printer is connected via USB)!