For some reason, a user suddenly cannot use the "NET USE" command to map network drives. Windows logon is working, but accessing network shares become very strange, with "System Error 2221 has occurred" message. This probably is a stored credential problem.
SOLUTION: Press your Windows' Start / Launch, in "Search programs and files" field type "Credential Manager" and you should see it shows up on the list. Run it.
Check the stored credentials and remove related credentials, by click on the "Remove from vault". Now, try your NET USE command to map drives again.