The connect procedure for imagePROGRAF printers can differ from the connect procedure for TDS/PlotWave/ColorWave printers.
You can also connect to a imagePROGRAF printer while Publisher Select 3 is open, in a similar way.
Make sure:
The preferred printer is connected to the network and switched on.
The driver for the preferred printer is installed and active.
Check this by printing a test page first.
Optional: When multiple drivers are installed and match the preferred printer, you can select the preferred driver from a list.
When you start Publisher Select 3 and you have selected a driver in the previous session, you can connect again to the required printer to display the list with available drivers.