In the 4.20 version of Dapper on the App Store, a bug causes Dapper to think it is not licensed properly.

I apologize for the problem this causes, it was through a bug on my part, and a fix is already in with Apple.

In the meantime, you can activate a 14 day trial and continue as normal. 

Once the fix is in, your Dapper will automatically recognize that you bought the full version originally.

Again, I am so very sorry for the issue.