I wonder if it might be feasible for the Preview screen to show the current communication status of the printer?
At present having set up the print I switch to the Preview screen and typically click the 'Begin Printing Over USB' button.
Whilst this works, occasionally I find that S3D has lost contact with the printer - which I can verify via the Machine Control Panel. In this situation rebooting the PC sorts out any problem with USB comms.
It would be nice if the Preview screen gave a simple status message for the printer.