AHA! I was getting the same error trying to import 1099s from Betterment, "That didn't work. Try signing in again. (103)"
After much searching, calling, waiting and talking with TurboTax support for 30 minutes (all to no avail), I started random "troubleshooting in the dark" and discovered that TurboTax didn't like my e-mail address!! (Of course it wouldn't tell me that)
If your e-mail address has a plus (+) in it, TurboTax will give you this very unhelpful error (it's probably converting the plus to some other character or removing it or something stupid before submitting the credentials).
Solution:
1. Go to Betterment and change your e-mail address (use an e-mail address without a + in it).
2. Verify the new e-mail address for Betterment by checking your e-mail and clicking on the link.
3. Ensure you can login to the Betterment website with the new address.
4. Go back to Turbotax and try importing from Betterment using the new e-mail address.
Hope this helps someone else... I sure wish *I* had that hour and a half back (kinda wish I'd just paid a real person to do my taxes now! Real people don't choke on a plus sign... dammit TurboTax!)
