Go to
Profile > Security Settings > Change user ID
Here you'll see the user ID (case sensitive) you need to enter to import your forms.
In my case I was receiving the error because my username is all caps but i was entering it with mixed case as when I created it, but E*TRADE changed it to all caps. Strange because I can log in just fine using my mixed case username on the web portal. Web portal login also works using upper case only username.
TLDR. Case sensitive username (try all uppercase) for importing via turbotax. Case insensitive username when logging in through the web portal.
