"I installed local::lib module and then tried to install Net::SFTP"

How? As I've asked before, be specific. You say you tried to install Net::SFTP but don't show how you tried to do this, or what when wrong. Did you read the link to the local::lib documentation I gave you? It looks like you haven't updated your code to reflect that fact that you want to use local::lib. Again examples in the documentation.