I'm trying to use vncviewer to log into lectura. It is asking me for a password. When I enter my lectura password, it says authentication failed. What password should I use?

When you run vncserver for the first time, you are prompted to create a password for vnc sessions.  If you have forgotten the password you entered, you can clear the stored password by deleting the /home/username/.vnc/passwd file:

lectura> vncserver -kill :nn    (where nn is the session number 
                                             assigned when you started vncserver)

lectura> rm .vnc/passwd       (remove existing passwd file)

lectura> vncserver                (you will be prompted for password
                                             to be used when connecting with vncviewer)