This didn't work for me. I tried to Log an employee out a few times, I received no errors but they were not logged out of QuickBooks.

The problem is caused by the Quickbooks Messenger Service.  When you log out of the company file, the QB messaging app is not terminated properly.  You can close it without restarting your computer.

Use CTRL-ALT-DEL and select the Task Manager.  Under the Processes tab, look for multiple instances of QuickBooksMessagine (32 bit).  Select each one and press Delete to terminate the process.  Close the task manager and log into Quickbooks.  It should now open the company file.