Hi savyk,
Since you are receiving that particular error message when you try to generate your token, it is indicative that your eBay account is already associated with an existing Auctiva account. If you contact our customer support team and let us know your eBay username, we'll be able to provide you with a solution to this problem.
If you have any additional questions or concerns, please feel free to contact our customer support team by completing the web form on the following page of our site: http://www.auctiva.com/Default.aspx
-Mike