W: GPG error: http://moff.mozilla.com fremantle Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 667387BFFF445C24 W: You may want to run apt-get update to correct these problems /home/user #
After that a new error came.................. When i typed: $ dpkg -r libwrt-api-experimental1 E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it. {actually I am trying to upgrade it to Android.}