Duplicate sources.list entry
After sudo apt-get update I got an error saying I got a duplicate sources.list entry.
Start a terminal:
gksu gedit
open /etc/apt/sources.list
open /etc/apt/sources.list.d/ and then look for the appropriate entry that's said to be a duplicate.
Check if they are the same and if that's the case enter a # in front of the duplicate entry. Then save the file an in another terminal enter
sudo apt-get update to check if the error has gone.
That's all there is.
I found some other usefull Apt tool here: a sources.list generator: