X11VNC - connection failed due to incorrect password even though password correct

Running Xubuntu 20.04 as VM on top of Ubuntu Server 20.04 with bridged interface. I am able to connect to the VM via SSH (also using Putty on Windows 10 machine that will access the VM). Using VNCViewer (part of the TigerVNC project) on a Windows 10 machine I entered the IP address of the VM. A popup for password is displayed where I enter the password but when I click connect I get TigerVNC An unexpected error occurred when communicating with the server: Authentication failure: password check failed! Attempt to reconnect? [No] [Yes] I installed x11vnc the usual way using apt. Following instructions online I created * an encrypted password file sudo x11vnc -storepasswd PASSWORD /home/USER/.vnc/passwd * an unencrypted password file echo PASSWORD > /home/USER/.vnc/password Respectively I executed x11vnc -forever -shared -display :0 -rfbauth /home/user/.vnc/passwd for the encrypted and x11vnc -forever -shared -display :0 -passwdfile /home/xubuntu/.vnc/passwd for the unencrypted password file. **Note:** Obviously I didn't do both in parallel. Also password typo is impossible due to the simplicity of the password (something like "abcd"). Both yielded the following log in the SSH terminal: x11vnc -forever -shared -display :0 -passwdfile /home/xubuntu/.vnc/passwd 30/03/2022 10:38:02 x11vnc version: 0.9.16 lastmod: 2019-01-05 pid: 6641 30/03/2022 10:38:02 Using X display :0 30/03/2022 10:38:02 rootwin: 0x53b reswin: 0x3800001 dpy: 0xc07a6840 30/03/2022 10:38:02 30/03/2022 10:38:02 ------------------ USEFUL INFORMATION ------------------ 30/03/2022 10:38:02 X DAMAGE available on display, using it for polling hints. 30/03/2022 10:38:02 To disable this behavior use: '-noxdamage' 30/03/2022 10:38:02 30/03/2022 10:38:02 Most compositing window managers like 'compiz' or 'beryl' 30/03/2022 10:38:02 cause X DAMAGE to fail, and so you may not see any screen 30/03/2022 10:38:02 updates via VNC. Either disable 'compiz' (recommended) or 30/03/2022 10:38:02 supply the x11vnc '-noxdamage' command line option. 30/03/2022 10:38:02 30/03/2022 10:38:02 Wireframing: -wireframe mode is in effect for window moves. 30/03/2022 10:38:02 If this yields undesired behavior (poor response, painting 30/03/2022 10:38:02 errors, etc) it may be disabled: 30/03/2022 10:38:02 - use '-nowf' to disable wireframing completely. 30/03/2022 10:38:02 - use '-nowcr' to disable the Copy Rectangle after the 30/03/2022 10:38:02 moved window is released in the new position. 30/03/2022 10:38:02 Also see the -help entry for tuning parameters. 30/03/2022 10:38:02 You can press 3 Alt_L's (Left "Alt" key) in a row to 30/03/2022 10:38:02 repaint the screen, also see the -fixscreen option for 30/03/2022 10:38:02 periodic repaints. 30/03/2022 10:38:02 30/03/2022 10:38:02 XFIXES available on display, resetting cursor mode 30/03/2022 10:38:02 to: '-cursor most'. 30/03/2022 10:38:02 to disable this behavior use: '-cursor arrow' 30/03/2022 10:38:02 or '-noxfixes'. 30/03/2022 10:38:02 using XFIXES for cursor drawing. 30/03/2022 10:38:02 GrabServer control via XTEST. 30/03/2022 10:38:02 30/03/2022 10:38:02 Scroll Detection: -scrollcopyrect mode is in effect to 30/03/2022 10:38:02 use RECORD extension to try to detect scrolling windows 30/03/2022 10:38:02 (induced by either user keystroke or mouse input). 30/03/2022 10:38:02 If this yields undesired behavior (poor response, painting 30/03/2022 10:38:02 errors, etc) it may be disabled via: '-noscr' 30/03/2022 10:38:02 Also see the -help entry for tuning parameters. 30/03/2022 10:38:02 You can press 3 Alt_L's (Left "Alt" key) in a row to 30/03/2022 10:38:02 repaint the screen, also see the -fixscreen option for 30/03/2022 10:38:02 periodic repaints. 30/03/2022 10:38:02 30/03/2022 10:38:02 XKEYBOARD: number of keysyms per keycode 7 is greater 30/03/2022 10:38:02 than 4 and 51 keysyms are mapped above 4. 30/03/2022 10:38:02 Automatically switching to -xkb mode. 30/03/2022 10:38:02 If this makes the key mapping worse you can 30/03/2022 10:38:02 disable it with the "-noxkb" option. 30/03/2022 10:38:02 Also, remember "-remap DEAD" for accenting characters. 30/03/2022 10:38:02 30/03/2022 10:38:02 X FBPM extension not supported. Xlib: extension "DPMS" missing on display ":0". 30/03/2022 10:38:02 X display is not capable of DPMS. 30/03/2022 10:38:02 -------------------------------------------------------- 30/03/2022 10:38:02 30/03/2022 10:38:02 Default visual ID: 0x21 30/03/2022 10:38:02 Read initial data from X display into framebuffer. 30/03/2022 10:38:02 initialize_screen: fb_depth/fb_bpp/fb_Bpl 24/32/4096 30/03/2022 10:38:02 30/03/2022 10:38:02 X display :0 is 32bpp depth=24 true color 30/03/2022 10:38:02 30/03/2022 10:38:02 Autoprobing TCP port 30/03/2022 10:38:02 Autoprobing selected TCP port 5901 30/03/2022 10:38:02 Autoprobing TCP6 port 30/03/2022 10:38:02 rfbListenOnTCP6Port: error in bind IPv6 socket: Address already in use 30/03/2022 10:38:02 Autoprobing selected TCP6 port 5901 30/03/2022 10:38:02 listen6: bind: Address already in use 30/03/2022 10:38:02 Not listening on IPv6 interface. 30/03/2022 10:38:02 30/03/2022 10:38:02 Xinerama is present and active (e.g. multi-head). 30/03/2022 10:38:02 Xinerama: number of sub-screens: 1 30/03/2022 10:38:02 Xinerama: no blackouts needed (only one sub-screen) 30/03/2022 10:38:02 30/03/2022 10:38:02 fb read rate: 230 MB/sec 30/03/2022 10:38:02 fast read: reset -wait ms to: 10 30/03/2022 10:38:02 fast read: reset -defer ms to: 10 30/03/2022 10:38:02 The X server says there are 10 mouse buttons. 30/03/2022 10:38:02 screen setup finished. 30/03/2022 10:38:02 The VNC desktop is: SZA-DT043-L-VM0:1 PORT=5901 ****************************************************************************** Have you tried the x11vnc '-ncache' VNC client-side pixel caching feature yet? The scheme stores pixel data offscreen on the VNC viewer side for faster retrieval. It should work with any VNC viewer. Try it by running: x11vnc -ncache 10 ... One can also add -ncache_cr for smooth 'copyrect' window motion. More info: http://www.karlrunge.com/x11vnc/faq.html#faq-client-caching One thing I noticed is that at least in the case of creating an unencrypted password file running x11vnc with sudo yields an error 30/03/2022 10:46:06 x11vnc version: 0.9.16 lastmod: 2019-01-05 pid: 6708 No protocol specified 30/03/2022 10:46:06 XOpenDisplay(":0") failed. 30/03/2022 10:46:06 Trying again with XAUTHLOCALHOSTNAME=localhost ... No protocol specified 30/03/2022 10:46:06 *************************************** 30/03/2022 10:46:06 *** XOpenDisplay failed (:0) ***x11vnc was unable to open the X DISPLAY ":0", it cannot continue ***There may be "Xlib:" error message above with details about the failure Some tips and guidelines ... I don't know how this affects the problem I am having but thought it might provide some insight to the more knowledgeable folks around here. Since it's an internal company network I am not worried about someone breaking into my VM (which is meant to be disposable anyway). I will try to setup X11VNC without any authentication (if possible) but even if that works I am still interested into the cause of the issue at hand.