Every so often, I come across a client that is leveraging the Message of the Day in their vSphere vCenter configuration. Usually, it’s a friendly reminder to disconnect any CD-ROMs an admin might have in use or reminding them to log out of the Windows sessions when done. Occasionally it is a legal disclaimer. (ugh!)
If you happen to be in the ‘I bought it so I am going to use every feature’ camp, be aware that if you have a self signed certificate that hasn’t been accepted by the client, you could run into this frozen session state. Unable to click ignore and unable to continue to the rest of your work. What's the hold up? A Message Of The Day screen HIDDEN behind the Security Warning.
ALT-F4 closes the Hidden MOD. (although since you didn’t read it, Lord knows what you might have agreed to). ;)