I didn't see any answers in that link at the answers forum - the guy said it cleared up on it's own (which it will often do). If it continues for more 24 - 48 hours or only some mail is affected:
Check the email addresses - are they valid?
Are Windows updates waiting for a reboot? If so, install and reboot.
Remove the account from outlook, restart outlook, then add it back. If using Outlook 2010 or older, uninstall the connector after removing the account then reinstall it using a fresh download.