During my first installation of ClearOS the (web) installer hangs during the system update step. It downloaded a lot but it didn’t applied the updates because of the error “Exception: Didn't install any keys”.
The easiest workaround to get rid of this is a manual update on a console. Therefore I switched to virtual machine and opened second console with ALT + F2 and logged in as root. With the yum package manager this is a simple task, run the command
yum update
Now the systems downloaded in my case around 100MB and applied the updates. During this the moment came where I had to confirm something with yes. After a while the system is updated and I could switch back to the browser with the installer.
It was necessary to went back to the previous step and also to reload the page once. Being back to the upgrade step the system now stated, that it is up to date and let me went to the next step..