This sounds like a variation on the same issue you had before. Can you try what jbl1120 suggested in the other post:
"I have encountered this issue before and have an easy workaround. Use Ctrl-F5 to to a hard refresh of the page. This usually clears the login issue and returns me to whichever page I was trying to reach."
ctrl-F5 will clear the cache of the site you are on, so do that after you get to our login page.
It seems like this happens when clicking on the link in the email. I would also suggest first going to www.grandslamfantasytennis.com, then hold down ctrl and F5 at the same time, then log in and click on the link in your to do list to edit your predictions.
Please let me know if this works. If it does not then I would be happy to log into your account for you to make your prediction while we get this fixed.