Go to system preferences / Startup disk and select the internal drive with OSx on as default.
Just highlight it and click restart.
NB .You may need to click on the padlock icon if closed and enter password before changes can be made
The machine should now reboot to your internal drive by default and cease searching for a network drive.
Tried all six steps and still getting this error message intermittently after a restart. Tried a few other things to determine what is causing this. The problem just surfaced a few days ago when connected to another computer that is not always on but on the same network. It has been fine like this for a couple of years up until the previously mentioned occurrence.