Hi feelexit,
The reason you are receiving that error message when you attempt to generate a token is because your eBay account is already associated with an existing Auctiva account.
Please contact our customer support team using the "File a Support Request" link on our help page, http://www.auctiva.com/free-auction-software-help/help.aspx, and we'll be happy to help you through this situation.
-Mike