My understanding is that there is a background process (ie. "watchdog") that is monitoring the parallel port driver performance. If the driver starts under performing, the watchdog alerts you to that fact.
This can happen because your machine has other processes competing for resources. Perhaps you're running other programs, your screensaver has kicked in, etc. You can either turn off the watchdog, or try and disable other processes/applications that may be interfering with the driver timing. If you're already running a very "clean" machine, then it might be telling you that you need more CPU power, RAM, etc.