This article describes about the error ‘Collectors with a newer version than the Core exists’.
Solution
In case Collectors are on a newer version than all Cores running this message will appear.
How to know if user has the latest version of Core or if there is a newer Core version available for upgrade:
In some cases there may not be a newer version of Core available and if that is the case user will receive an upgrade as soon a possible.
If a newer version is available in the link above, create a FortiCare ticket and request an upgrade.