[WTA] warning: rpmts_HdrFromFdno: Header V3 DSA signature: NOKEY, key

Kenapa ya waktu install aplikasi misal nbtscan di clearos saya seperti ini ???
saya juga mau install zarafa juga sama

"warning: rpmts_HdrFromFdno: Header V3 DSA signature: NOKEY, key ID 217521f6

GPG key retrieval failed: [Errno 5] OSError: [Errno 2] No such file or directory: '/etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL'"