I'll take a chance on answering this:
Perhaps the user has opened a file (not in the Vault) and the EPDM log-in screen appeared. (This often happens to me after first logging into Windows 7.) If the user then cancels the log-in (because he/she is not trying to access the Vault) the following dialog appears warning that automatic login will be disabled:
If this is the case, trying to open the Vault folder afterward results in nothing happening—no log-in dialog appears.
The only way to log in and access the Vault is either to use the EPDM icon in the Notification area, or to kill the process "EdmServer.exe" in Windows Task Manager:
Killing that process will result in the EPDM log-in dialog appearing automatically when the Vault folder is accessed.
Hope this didn't answer the wrong question.
You only need to Right Mouse Click the Vault View Icon and Select Log In.
There should be no need to kill the process.
After doing as Kip says, you'll still need to click again on the vault icon/folder.
I agree it's better to use the icon, and maybe from version 2013 on it will never be necessary to use Task Manager. There were times in the past when no other remedy would work.