Most of the time, this is caused by a poor connection to the cloud server, or you have connected to your server session from a new device.
Re-establishing your connection to the server will resolve these issues, if you are still unable to print after reconnecting, please submit a support ticket.
Logoff or Sign Out by either clicking the red 'Logoff' button or by right-clicking on the 'Windows Key' and then clicking 'Sign Out'.
DO NOT click the 'X' at the top of your session window as this only disconnects you from your server session. This is to say that your session will still be active on the server and will not re-establish your connection.