The application is still available for downloading, but you will have to contact the developer to get another key for the product. It's possible that the key was valid only for the version released at that time. I recommend contacting him, because he's the only one who can issue you a new key for the software you have.
Use one of the following email addresses to get in touch with him:
- Sales Team: email@example.com
- Technical support: firstname.lastname@example.org