dpkg? Hmm so it's a problem with packages. Would you have not with your command in the terminal open another program of package management like e.g Synaptic? If yes, close it before use your command in the terminal.
K.I.S.S. ===> "Keep It Simple, Stupid"
"Simplicity is the ultimate sophistication." (Leonardo da Vinci)
"Everything should be made as simple as possible, but no simpler." (Albert Einstein)