This error has a number of potential causes:
Maple was installed on a new machine, but the activations for the Purchase Code have been exhausted.
Typically, Maple can only be installed on one machine, but Customer Service can grant an additional one in some cases (or reset the code if necessary). Please contact email@example.com for more information.
Maple was installed on the same machine as before, but the operating system has been changed or upgraded. Please contact firstname.lastname@example.org so that they can reset your Purchase Code.
Maple was installed with a temporary license, but later, the license was converted to perpetual (for instance, student status was validated), and it won't reactivate properly.
Your license file will need to be modified, so please contact email@example.com with your purchase code (and possibly your host ID).