Hi redback_opals_australia,
Given the course of events you have described, it sounds like eBay must have revoked the token associating your Auctiva account with your eBay account. To correct this problem, you'll just need to generate a new token within your Auctiva account, which can be done by clicking the "eBay Settings" link under the "My Account" tab within your account, and then clicking the "Get New Token" link on the ensuing page.
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/help/requesthelp.aspx-Mike