When registering Zend Guard using valid local license file, you get invalid license.
In most cases, this is because the user running Guard application has insufficient permissions to write to the installation directory, normally under "C:\Program Files (x86)".
The Workaround for the above common problem is to right-click "Zend Guard" shortcut, click "Run as administrator",perform the registration using help -> register menu, and finally closing Zend Guard application once registered. The next time Zend Guard will be opened by a regular Windows user, it will already be registered.
Please review the following KB article, elaborating on additional options for invalid license: