There are several different messages that indicate you may have an invalid key which may be displayed.
You will receive the "invalid" error message if:
You have a trial version of the software already installed. You must uninstall the trial version first and then install the new software.
There was a typo while entering your product key during installation/activation. It is recommended that you copy and paste the product key rather than type it out.
If you still require help, contact support by clicking the Contact Us link at the bottom of the Help page.