Red Hat Subscription Manager で登録したシステムで yum update を実行すると Errno 14] PYCURL ERROR 22 - NSS: client certificate not found エラーが発生する

Issue

• Red Hat Subscription Manager で登録したシステムで # yum update を実行すると以下のエラーが発生します。

Loaded plugins: product-id, security, subscription-manager
Updating certificate-based repositories.
[Errno 110] Connection timed out
Repo rhel-6-server-rpms forced skip_if_unavailable=True due to:/etc/pki/entitlement/5337781872319746256.pem
Repo rhel-6-server-rpms forced skip_if_unavailable=True due to:/etc/pki/entitlement/5337781872319746256-key.pem
Repo rhel-6-server-cf-tools-1-rpms forced skip_if_unavailable=True due to:/etc/pki/entitlement/5337781872319746256.pem
Repo rhel-6-server-cf-tools-1-rpms forced skip_if_unavailable=True due to:/etc/pki/entitlement/5337781872319746256-key.pem
https://cdn.redhat.com/content/dist/rhel/server/6/6Server/x86_64/cf-tools/1.0/os/repodata/repomd.xml:[Errno 14] PYCURL ERROR 22 - "NSS: client certificate not found:/etc/pki/entitlement/5337781872319746256.pem"
Trying other mirror.
https://cdn.redhat.com/content/dist/rhel/server/6/6Server/x86_64/os/repodata/repomd.xml:[Errno 14] PYCURL ERROR 22 - "NSS: client certificate not found:/etc/pki/entitlement/5337781872319746256.pem"
Trying other mirror.
Setting up Update Process
No Packages marked for Update