Sometimes when you finish a print job, the printer ``Ready'' light keeps flashing for a minute or so. Somehow, the printer has received some character(s) after the control-D which was sent immediately after the PostScript file. The most common is that a newline has been inserted after the control-D. The printer took these character(s) to be another program, and eventually timed-out while waiting for the rest of it. This can happen because of the host not waiting for the printer to finish.