Three days ago - no one can get to their shares. From the server, there appeared to be no users. Found SERVER service disabled and NETLOGIN service stopped. I needed to set the SERVER service to Automatic and start it, and start the NETLOGIN service. Then I needed to recreate the shares.
Today, it happened again. Users were fine for an hour into the work day....then they couldn't get to their shares....I needed to start both services again, but didn't need to recreate the shares this time. The eventviewer logs were no help - seemed to be purged and started up again at the moment I believe the shares disappeared. I increased then size of the event logs for next time (they were 20,000KB).