I am not able to resume a session after the screen has been locked for a long time. This is not a new problem. Similar questions have been posted in the past, two of which are listed below.

Black Screen after Screen Lock

Screens don't work after shutting off

This problem has also been reported to Ubuntu, who have provided the following wiki link for guidance.

DebuggingKernelSuspendHibernateResume

One cause of the problem that is noted in DebuggingKernelSuspendHibernateResume is when the swap file is encrypted. This will automatically happen if one decides to encrypt the /home directory during installation. As I did not choose this option, I don't believe that my swap file is encrypted, however, I have encrypted the home directories of the Windows XP partition which resides on a separate drive. Not sure if this is an issue but, how would I be able to determine whether or not the swap space partiion under Ubuntu has been encrypted?

The solution noted by @cprofitt in his/her answer to Screens don't work after shutting down mentions modifying xorg.conf, and possibly grub. Unfortunately, I cannot locate the xorg.conf file on my system. It is not in the typical locations that one would expect to find it (e.g. /etc/X11). Also, I am not certain how to modify grub.

As a workaround, I have turned off screen locking, however, I would really like to solve this problem. My configuration is as follows:

Ubuntu 11.10

VGA compatible controller: Intel Corporation 82865G Integrated Graphics Controller (rev 02)

Also note that I have a KBM switch that switches between the PC and a Mac OS X laptop. I know for a fact that this is not a problem since, I am still able to switch to my laptop when the problem occurs. Furthermore, I have physically connected a keyboard and mouse to the PC where I have installed Ubuntu, and the problem still occurs.