The error (3015) means that the serial number that you are attempting to use, does not match the software version you currently have installed. This typically occurs if you attempt to activate an older version of 3D Issue with your new serial number or vica versa.
Another possible reason why this error might appear is that you possibly entered the serial key incorrectly. We would advise copying and pasting the serial key, as it is case sensitive and to ensure no additional blank spaces are copied before or after the serial key.
If you further problem with the error, please contact support@3dissue.com