Look carefully at the application name in that error message, and at the name of the application that you have installed and are trying to register.
There is no application named DEVONthink Express. You must have misread the error message.
There is no application named DEVONthink Pro Personal. Look at the application name in the menubar. What is the name of the application? What is the name of the application for which you purchased registration, as displayed in your license code email message?
To solve the license problem the best way is to send me the license code to email@example.com. I’ll check your license code, if it really shouldn’t work, I will create a new one for you as a replacement.