Hi there,
It could be one of two issues. The first release of HoneyDew has a bug where even if you enter your reg code in some cases it will expire anyway. It's fixed in the version 1.0.12, you can check your version in the 'About' screen. If you need to upgrade to 1.0.12 you can do it at this site:
http://ota.versatilemonkey.com/honeydew/It should fix it for you. You can install it right over the old one.
If you are running 1.0.12 or later, did you make sure to enter the registration code you received after purchasing in HoneyDew's settings screen?