The most common cause of this error occurs when you have already installed ChimpRewriter on two computers. Occasionally, if something changes on your computer, it can look like you have it installed on a different machine. Never fear. this is an easy fix :)
Simply log in to the user management page at http://account.akturatech.com. You will find your current activations as well as a link to deactivate them. The last activation date is also listed, and your best bet is to deactivate the oldest one. Then you should be able to register on the new PC.
Bear in mind that you can only deactivate once every hour.
If these options didn't work, contact us and we will look into it further!