Sitefinity will be throwing the trial message if the system is not licensed or licensed properly.
A possible reason for the warning is if you have changed the host header thus making some routing and our code cannot validate the key. Verify if any internal routing is applied or some firewall/IP restrictions are messing up with the licensing service.
Please note that you need to register a domain in our system for your license, so that the system knows whether the domain that is being used is licensed properly.
the Telerik team
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items