Login on Putty SSH using root Access and type the following commands.
Step 1: type the commands pgrep vnc and there will be show some number bellow after you type the commands.
pgrep vnc
Step 2: the number show is the number ID of the running VNC on the system. so you need to kill it to close all running vnc by typing kill ID.
kill Number_ID
Step 3: type reboot to reboot your system.
reboot
After that you can now allowed to use the VNC without the Authentication. if this solution not work
Open a Ticket Support or message on Live Chat System.
Thank you ^_^