OK. I think I solved the problem. Poor communication between the MP and Magic Box I post the solution to the problem, if it can help someone.
If your listings are showing as Unavailable on your Manage Inventory list or the sales of all of your products are failing then there is an issue with the Marketplace communicating with your Magic Box in world.
I am including the steps here to fully reset your Magic Box. If this does not correct the issue, please ask to have the region where your Magic Box is locate restarted then reset the Magic Box again.
This should fully restore all of the communications between the Marketplace web site and your Magic Box on the region.
Make sure you are using the most recent version of the Magic Box, located here: https://marketplace.secondlife.com/p/Xstreet-SL-Magic-Box/36791
1. Go to your Magic Box Status Page that is linked under your Merchant Home Page on the Second Life Marketplace and remove all of the Magic Boxes you have listed there.
2. Go in-world and "Touch" each Magic Box and select Reset from the popup menu that appears.
3. Wait. Do not reset your Boxes again during this time or you will risk having your Box show up with incorrect data and your items will remain inactive). The Magic Box colors will change during the communication process. Once the Magic Box returns to the default color, the communication process is complete and the Magic Box should be re-linked to the web site.
4. After the Magic Box color changes back to the default, go to your Manage Inventory page on the Second Life Marketplace and click on the "Sync Marketplace with Magic Boxes" button located on the right side of the page.