The key I've received from the developers can't activate the program.
There are three possible cases why you can't register the application:
You mistyped the serial number. Double check the serial number and enter it again.
The serial number is wrong or used. Contact the developers and explain the situation.
You need to allow AcroRIP communicate with the online servers. Access your firewall and add it to the Exclusion list. This should give exclusive access to reach the activation servers if online activation is necessary.