That banner was added because there's a bogus LW update showing up in search results. It's a 75.7 KB .exe & shows up as "Urgent LW update - download & install now". If people download & install that thing they could end up infected. So, to make sure everyone knew that it was crap, the warning banner was added.
It's just to make sure everyone knows what's a real LW update & what's not.

The padlock symbol doesn't apply to music or video etc

What happens when you try to download? If files aren't moving to the download pane, it's probably a license issue.
License (click)

If files get stuck connecting for ages & then need more sources forever, it's possibly fake files.
Fake files showing up in search results

If absolutely every file you try to download does this (do a test & try to download an old song with a modem source), delete LW's preferences folder when LW's completely closed. See point 3 below, also point 2 if you've used much older versions of LW in the past.
Fixes for LimeWire
Deleting that folder will kill all of your settings within options, you'll have to go back through & reset things afterwards