I am using vnc server for the first time on Ubuntu with gnome (Ubuntu 10.04.2 (lucid) with Gnome 2.30.2) and have a strange login issue. When I ran it the first time, I was asked to setup a password. I was subsequently able to connect to the :1.0 display from a VNC client after entering the password I setup earlier, and it seemed to work as I expected. The issue is that once the session times out and the Lock Screen is presented, I can no longer login. My regular Linux password gets rejected and I even tried the VNC password, just in case it gets setup differently here. This happens every single time, and I reproduced it multiple times. I am able to lock and unlock the session on the physical display monitor with no problem. Can anyone give me a clue on what might be going wrong here?
Your gnome session may be setup without privileges to access the password database. Check
See my answer to Best fullscreen solution for vnc on linux for some alternative configurations which should work with locking. Using xinetd to run VNC will drop your session if you disconnect. RDP allows you to disconnect and reconnect without loosing your session.