Check to see if your Internet Options, General Page, Temporary Internet Files Settings Tab is set to "Check for newer versions of stored pages - Automatically". Can you ping the Unity server by hostname from your workstation, using the URLs you posted? See if you can do same using the IP address instead, i.e. http://x.x.x.x/web/sa. We occasionally see this error and validate DNS is working fine. The quick fix is to delete/recreate the bookmark.
It does sound like a DNS problem so I'd check it by IP like Ginger suggested. Also check your bookmark and be sure it's just http://dcunity1/web/sa. If you created the bookmark after you were logged in, the URL is gonna be something like http://dcunity1/web/sa/FrameASP/StartFrame.asp and I've seen that cause an error if that's your bookmarked page.
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...