Hi all,
It is correct, the key has expired. Please import the new public key from the repository by following these steps:
## You will the following warning: NO_PUBKEY 07BE4CBFFDE85677
sudo apt-get update
## Installing a required package
sudo apt-get install gnupg2
## Downloading the new public key
sudo wget -O -
http://keys.zentyal.org/zentyal-6.2-packages-org.asc | sudo apt-key add -
sudo apt-get update
We will publish shortly a new ISO to avoid new installations to be affected by this. Best regards.