At the top of my monitor there is a Red Triangel with an Exclamation mark What is This?

Red Triangle with Exclamation mark inside I Clicked on it a Box poped up, inside it says That "you may have a problem caused by the Network or by a Respository that is no longer avilable". Please update manually by clicking on this Icon and then selecting"Check for Updates" and chech if the listed respositories fail. Then in Bold Type SHOW UPDATES INSTALL ALL UPDATES CHECK FOR UPDATES PREFERENCES So I did what it said to do It took me to another Screen I followed through A Box Poped up UPDATING CASH a Red Line kept going Back & Fourth a few times then stoped and Gave me a message which read Failed to download respitory information there was a small box DETAILS so I clicked it there inside Read E: Problem executing script APT: : Update: : Pre-invoke'if [-x/usr/bin/daptup]; then/usr/bin/daptup-pre;fi;E:Sub-process returned an error code What the heck does this mean & what can be about it? I just don't know or even understand it. Please Help Me!