Hi kryptoknight,
To add the template to your listings after they have already been posted, please revise each listing for which you would like to accomplish this via the following process:
1) Locate your listing in your Saved Listings folder, make any necessary changes(select template), and save.
2) Check the box next to your updated listing in your Saved Listings folder and click the “Get html” button.
3) Select All and copy the html in the popup window.
4) Locate the item on eBay and click the "Revise Item" button.
5) Click "Edit Description" then click the "Enter your own html" tab above the description editor.
6) Delete the html that is already there and then paste the copied html in its place and save you changes.
The "404 Error" you are receiving sounds like a browser related issue. Please file a support request regarding this problem using the appropriate link on our help page:
http://www.auctiva.com/free_auction_software_help/help.aspx-Mike