Could you just confirm that my understanding is correct : You are unable to connect to Tableau Online with Tableau Desktop because of the error "10029"
1. Do you know when your Tableau Online account started ? Following the error message, I believe the trial expired (i'm not 100% sure).
I think you should be able to see the expiration date on your Tableau Customer Portal: http://customer.tableausoftware.com/
2. Try to reach one of our sales account rep, even if your site expired, they will be happy to help you : Contact Us: Tableau office contact directory