Update: It seems if I had done a little more detective work, I would’ve been led to PixelBreaker’s blog post about this very problem. It seems it’s an error involving ScreenTime, the packing software used to bundle PolarClock into the screen saver format for OS X Leopard.
The problem only occurs if you have a multiple-monitor setup. The easiest solution is to open your Screen Saver preference pane and check “Main Screen Only.” This way PolarClock is only displayed on your main display and not the others, and the error does not occur. Simple enough!
The Problem
Late last week I started encountering the weirdest error on Leopard, Mac OS X 10.5.7—my shortcuts using ⌘ (Mac OS X’s Command button) stopped working. This isn’t a good thing for me because my workflow depends on two shortcuts using ⌘, which are ⌘+Tab (for switching between open applications across six Spaces on two monitors) and ⌘+Space (set for Quicksilver, which allows me to quickly open applications and interact with them on an amazing level). Also affected was Exposé—I was unable to use my hot corners or Exposé functions.
The Witch Hunt Begins
I figured out that a reboot of my MacBook Pro solved the issue, but only temporarily. It seemed like it would occur within an hour of a reboot.
Tonight I decided I’d take no more, and opened up OS X’s wonderful Activity Monitor (located in ~/Applications/Utilities/). I should’ve done this long ago (I might have done so but just neglected to see the error). Here, I quickly saw a potential cause—OS X’s ScreenSaverEngine process was hung. [Click thumbnail for full version.]
After force-quitting the misbehaving process, I remembered that about two weeks ago I downloaded several screen savers and installed them. I set my screen saver to a default Apple screen saver and deleted a few of the screen savers I had downloaded. Immediately I was granted the gift of my ⌘ shortcuts again.
Point Fingers at Possible Criminals
After some time rejoicing, I reset my screen saver to pixelbreaker’s PolarClock v2 and left my computer, giving the screen saver a chance to start. I returned to my Mac a few minutes later and ended the screen saver, and guess what? That stupid ScreenSaverEngine process was hung up again. I looked at the detailed process information and I thought it may have something to do with the screen saver database cache, and not the Polar Clock screen saver. So I deleted the com.apple.ScreenSaver.Engine/Cache.db file, hoping it was just corrupt. [Click thumbnail below for a partial list of open files and ports involved, taken from Activity Monitor.]
Using my still functioning ⌘+Space, I told Quicksilver to launch ‘ScreenSaverEngine,’ automatically launching the screen saver, just like it would if it would’ve started by itself. After stopping the screen saver, the ScreenSaverEngine process hung again, killing the ⌘ shortcuts and Exposé.
Back to Basics & Verdict
I changed my screen saver to Apple’s ‘Flurry,’ initiated ScreenSaverEngine, and ended the screen saver after several seconds. My ⌘ shortcuts and Exposé stayed functional.
So, concluding, this error seems to rest within either the Polar Clock screen saver specifically, any user-installed screen saver, how the ScreenSaverEngine database works (possible corruption), or some combination of these elements.
If you have any ideas or have had a similar situation, comment below.