I have an iMac running Mac OS 10.6.8 with fast user switching enabled, Vine VNC server running on one user account, and the login screen displayed. The screensaver on the iMac activates but then freezes sometime later, so that the display never goes to sleep. I can access the desktop associated with the logged-in user without problem, so the computer itself is running just fine, although accessing it remotely doesn't cause the screensaver to stop (or start, or wake up, or do anything).
The iMac uses a battery operated keyboard and trackpad, so I leave them turned off whenever I'm not using the machine locally (which is most of the time). If I turn them on, the screensaver immediately disables and the display returns to the login screen. However, the point of the VNC setup is that I often am not around to turn the keyboard on for five seconds and then off again.
The problem isn't really preventing me from using my computer, but it is causing the display to remain on (with the same image displayed) essentially 24/7 whenever I'm not around, and besides that is slightly worrying since no part of the computer should freeze... So my question is,
Why is the screensaver (and only the screensaver) freezing, and how can I get this to stop so that the display will go to sleep?