Red minus symbol on top !

[chandramouli-r]

Red minus symbol on top shows problem occured while checking updates.
When executing
sudo apt-get update and sudo apt-get upgrade it works fine.

[Impavidus]

So, what's the complete output of
sudo apt update
sudo apt upgradeMaybe it was a temporary server or network problem that was fixed automatically, maybe you have to do something to fix this.

BTW, that white bar in a red circle is, to those familiar with the Vienna convention on road signs and signals (https://en.wikipedia.org/wiki/Vienna_Convention_on_Road_Signs_and_Signals), also known as a no entry sign. Many icons in Ubuntu seem derived from traffic signs, although it isn't always clear why a particular sign was chosen.