Customers are entitled to the number of activations equal to the quantity of licenses purchased. For example, if you have (5) production licenses that would allow you 5 activations. 

Customers get this error because all activations are currently in use. To resolve this issue please deactivate the serial number from the current server. Once this is done retry the license activation. 

If you would like more details on deactivating a license please see the License Manager Reference which can be found online at the following link: License Manager Documentation 

For additional help please open a ticket: