Have all users close QuickBooks and log out of the server. The server admin will need to follow these steps:
1. Open Task Manager on the server (or services.msc)
2. Go to the Services tab (you may need to choose "More Details")
3. Click the Name column to sort the services by name
4. Scroll down to the services starting with the letter Q
5. Right-click and restart the following services
QBCFMonitorService
QuickBooksDB## (the ## will be your QuickBooks year plus 10. For example, QuickBooks 2017 is QuickBooksDB27)
6. Right click on each service in the red box (from above screenshot) and click on "Properties" from the menu shown.
7. In the Properties dialog box, change from "Manual" to "Automatic",
8. Click "Apply" and then click "OK" to close the window and do same for the other versions of QuickBooks that are displaying stopped or Automatic.
Customer should now be able to open the company files again.
Additional troubleshooting if issue persists
Open file doctor
Select the affected company file
Run the check on the file
Company file should be repaired
Screen shots below for reference
Additional reference links