Symptoms
Trying to activate a FineReader Engine 12 license through the License Manager, you can get the error This serial number cannot be used to activate ABBYY SDK 12:

Cause
The reason for such behavior is connected to the license protection type: the license uses online protection, which does not require activation.
Resolution
Please specify the appropriate license parameters during the initialization: Project ID, license path and password.
For more information, please refer to the FineReader Engine 12 Online Licensing article.