There is temporarily a problem with the Clearcenter proxy server so for the moment a fresh install from the 7.7 iso will not be able to update or access the marketplace. As a workaround, please perform a manual update of yum-marketplace-plugin:

rpm -Uvh http://mirror1-newyork.clearos.com/clearos/7.7.2.280072/updates/x86_64/RPMS/yum-marketplace-plugin-2.4-1.v7.noarch.rpm

This will allow yum and the marketplace to work again.

An alternative workaround is to install with the 7.9 RC iso

Note this issue may also apply to any installation not yet updated past ClearOS 7.7.

This issue does not affect people on 7.8 or 7.9 and only affects some users on 7.7 and all users on 7.6 and below.