You can dump lassas direcly from task manager or use procdump,in this case you are a local administrator on machine but you have not full admin token,i.e task manager is not running as administrator on windows 7 and you did not invoke UAC (consent.exe),then you can use mimikatz to grab LSA secrets.Use this link it is useful https://forums.hak5.org/index.php?/topic/29657-payload-ducky-script-using-mimikatz-to-dump-passwords-from-memory/