This is a software issue, not eBay. Using the web based bidder I can link fine and didn't have any token problems. I've changed eBay password as well. Also, when entering the registration key I get the infinite wait icon and it never acknowledges it being properly entered...this may be a separate issue. Right now, I've paid for a software launcher.
BTW, the network check passes, fails only on login.
I think we already discussed it in the support ticket.
You need to make sure to use the same username you login to the Web version as well as when you login using the Windows app.
Please let me know if any questions.