This article explains what actions to take if you see the error message “This Display ID is in use by another Display”.
Verify that you do not have multiple Displays using the same Display ID
The most common reason to see this error message is multiple Displays using the same Display ID. Each Display ID is intended to be used with one Display. If you have not created a Display ID for each of your Displays, please see the Displays article subheading To add a Display using a Display ID.
If you discover that you have configured two Displays with the same Display ID, please see the article How to Change a Display Id on a Media Player.