Which print button did you click? You need to click the one just above the invoice within the Manager window. You cannot click or use shortcuts for the operating system’s normal print function.
For my previous case, my printer is connected to my office’s server, the server was not responding, and I have set the server printed as default, that is why it couldn’t respond.
What I did was, restart the server which my printer is connected to and it all became alright after that.