The license serial number can only be activated once.
1. It is possible that you are trying to re-generate your registration and activation code using your 12-13 digit serial number. If this is the case the serial number can only be activated once. Please check your emails for the license information that will include NAME, LOCATION or EMAIL, and REGISTRATION CODE. If you cannot find an email with this information please contact our support department using the form below, including the name the software was registered to, date purchased and the full license serial number. You can also recover your registration code using the automated utility at https://www.nch.com.au/support/reg.html?display=keyrecovery#EEEli
2. This error can also occur if more than 13 characters are entered into the field. This includes spaces at the beginning or the end of the number.
3. If you are trying to re-activate your license after a computer crash you will need to contact support using the form here.