from which KNIME Analytics Platform version did you upgrade? With KNIME Analytics Platform 4.0 we moved the EXAMPLES Server to KNIME Hub, whereas for older versions we still use the previous EXAMPLES Server. Have to tested it with a fresh installation of KNIME Analytics Platform?
Do you know if you are behind a firewall that might block the fetching of the content for some reason?
Are you able to connect to My-KNIME-Hub (simply use your forum login)?
Does the error still occur?
We will also check if there has been some problems with KNIME Hub around that time.
Btw., you can also export and import your preferences into an .epf file in case you want to backup your KNIME preferences, in case you ever have to re-install it.