run sudo apt get update and gives error

[Mohammad_Javad]

Hi

When i write sudo apt-get update in Terminal i give this error




Fetched 177 kB in 1min 27s (2,031 B/s)W: GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4874D3686E80C6B7
W: GPG error: http://ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A1715D88E1DF1F24
W: Failed to fetch http://ppa.launchpad.net/pcf/miro-releases/ubuntu/dists/trusty/main/binary-amd64/Packages 404 Not Found


W: Failed to fetch http://ppa.launchpad.net/pcf/miro-releases/ubuntu/dists/trusty/main/binary-i386/Packages 404 Not Found


E: Some index files failed to download. They have been ignored, or old ones used instead.


how can fix it ??

[grahammechanical]

PPAs are useful for installing certain software that is not available in the Ubuntu software centre. After installing the software I always disable the PPA in Software and Updates.