Weird screen saver problem

[Gregory Seidman]

My MacBook Pro (running 10.5.4) has been occasionally showing a black
screen when waking from sleep (opening the lid and entering my password to
unlock). The pointer is visible, however, and moves normally with the
touchpad. If I close the lid to put it back to sleep then open it again,
after I unlock it everything seems normal... except the screen saver never
starts under any circumstances.

Running
/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine
from the commandline exits immediately with no output and does not leave a
process running. Using the Start Screen Saver action in Automator fails
with a content-free error. Hot corners to start the screen saver are
ignored. All I get in the console log is a cryptic "Screen saver is running
in blackout mode."

Logging out and logging back in fixes the problem, but I'm hoping someone
knows of another way to revive the normal operation of the screen saver.

--Greg