@fossette Thanks for your advice, but sometimes there are networks which you need to use that you can not change, because the owner is not you
And WEP is still a valid encryption method, albeit insecure.

@Gayan-Priyanatha Same problem for me. At a customer site they are using WiFi with WEP and a code like 429a2936580b72330486c13973. Trying to configure this yields the following result:

 root@Omega-5857:~# wifisetup add -ssid Visitors -encr WEP -password     429a2936580b72330486c13973
> Restarting wifimanager for changes to take effect
root@Omega-5857:~# wifisetup list
{

    "results": [
 {
    "ssid": "xxxxxxxxxxxxx",
    "encryption": "WPA2PSK",
    "password": "yyyyyyyyyyyyyyyy" 
},
    {

    "ssid": "Visitors",
    "encryption": "WEP",
    "password": "1" 
 } 
] 
}