It may be possible you are trying to activate with a valid license key, but are trying to do so with the wrong version of our software. We offer several different software programs, so please make sure you try to activate the right version of the software you purchased to match the program's license key - MOBILedit Phone Manager, MOBILedit Forensic Express or Phone Copier Express.
You can download the software here:
http://www.mobiledit.com/downloads