I haven't seen this one before, but searching a bit on the Internet suggests it could be:
1. A bad PostgreSQL driver on the host you're using Tableau on
2. You might not have opened up the "readonly" user on Tableau's PostgreSQL repository (see "repository access on page 6 of the Install_guide.docx )
3. You are putting in the wrong username / password into the connection
I have tried mentioned steps in Install Guide then only am getting this error.
The following Error occurred when i try to connect VIZSQL. Please find the following error
Communication closed during authentication; Socket has been closed. Invalid username or password.
Now its working fine, I have reinstalled both desktop and server then configured again.
Thanks for sharing what fixed it!