After installation, I checked to share my d: drive. Inside containers I did not see files. That was problem #1.
Then I restarted the machine (I thought it did not catch the changes properly because it is Beta), and on starting Docker again, the d: drive was no longer selected for sharing. Checked d: again, was prompted for username/password - but it would not accept it (that part at least worked on first attempt). So I am basically stuck at this credentials prompt.