Hello,
i did have the same problem, this is what worked for me:
The problem seems to be that yum can not retrieve the mirrorlist for the repository.
http://mirrorlist.clearos.com seems to be unavailable.

So i went ahead and modified the repo file /etc/yum.repos.d/clearos.repo to use the baseurl and not the mirrorlist
by commenting out the mirrorlist (#) and activating the baseurl (remove #) for all contained repos



Since i also got the error that the *paid repos could not be found and i did not find where they were defined, to disable them i created a workaround for that too.

I created a new file /etc/yum.repos.d/paid.repo

with the following content:


this will disable the missing *paid repos and the marketplace and repolist will work again.

cheers