Unpause your printer
Printers will not print or calibrate if they're paused. Depending on the model of your printer, you'll see different indicators if the printer is paused.
T800: "OFFLINE" in top-right corner

The OFFLINE text means the printer is paused. Unpause it using the green pause button [ I I ] below the screen. If prompted to save settings, choose Save Permanently in Active Config. You should then see ONLINE in the top-right corner of the screen, meaning the printer is ready.
ZD621R: Pause indicator above screen

If the PAUSE light is lit up yellow, the printer is paused. Unpause it using the Pause button [ I I ] to the right of the screen.
ZD500R: PRINTER PAUSED message flashing on screen
If the printer's screen flashes PRINTER PAUSED, unpause it using the Pause button [ I I ] to the right of the screen.