Without a valid license, most iZotope plugins will operate in "Demo Mode" or "Trial Mode." This usually means that audio will periodically mute, or specific features will be locked. The license file unlocks the full potential of the software, removing these restrictions.
If you're troubleshooting, it helps to know where iZotope keeps its data. By default, presets and documentation are stored in your User Documents folder C:\Users\[User]\Documents\iZotope Macintosh HD > Users > [User] > Documents > iZotope How to authorize your iZotope software Izotope license file