2c53b37 commented

I have just updated to v. 7.0.2 n]and have tied to register using my Cyberduck registration but I get an Invalid Registration note on my About Cyberduck dropdown menu.

Please advise how to rectify this problem

@dkocher commented

The donation key file must have been modified when saving it from your email application. 
 * If you are using a webmail provider, try using a different browser or email client application to access your mail. 
 * Forward the mail to a different mail account where you possibly don't have an issue downloading attachments.

You can always lookup your registration key at https://cyberduck.io/help#recover to receive it with the email address registered.