Printer sends after each received command an "ok" so we know it was read and we send then next command. If we miss "ok" print would stop therefore. So if after timeout we still got no ok we send message and send next command anyway assuming there was a communication error. Check log with enabled commands and ack if you get anything from printer after new commands get send. If not the serial connection is defect - hang on serial driver or firmware or... Fact is just that host does not get any responses any more. If this keeps happening think about other usb port, shorter or better shielded usb cable. Often electric noise is the problem.
