While I was trying to update my fedora release I got the following error:
GPG key retrieval failed: [Errno 14] curl#37 - "Couldn't open file /etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-x86_64"
Therefore my update could not finish. I was also not able to install anything using yum due to the same error.
I'm running of Fedora 21 (recently updated from Fedora 19 using fedup).