This is what worked for me:
Step 1: Log in to schwab.com with your browser. Do not autofill with a password manager. Copy paste your login and password from wherever you have them stored or just type them in if you don't have them stored anywhere.
If Step 1 gets you into the site then you can be sure the problem is not login and password. If you cannot log in that way then fix your login and password.
Step 2: Close TurboTax.
Step 3: Re-start TurboTax
Step 4: Go to the download area and start the process. It may ask you to log in the intuit.com to make sure you are authenticated.
Step 5: Login to schwab.com from TurboTax
Step 6: Select what accounts you want to download data from.
That should do it.
