Unlike the original Mac OS, Mac OS X has a system of preference storage that involves a programmer-friendly, user unfriendly construct, the plist. Plist is short for "property list".
With fairly regular frequency, these preference files or "plists" get corrupted under Mac OS X. Worse, the corruption is largely undetectable with plists. This means that the plist file can become corrupted, the operating system facilities can't tell, the application tried to read the plist and digest the data, the corrupted data gets into the app, the app malfunctions, no clue as to why except some crazy error code that was eventually generated within the app because of an operation that went bad because a long time before, there was undetectable garbage read in from the plist file.
Ok, here is the good news. The preferences or plist files can be deleted and the worst case is that you lose some of your app settings you modified, usually through the "Preferences" menu item under the menu named after the app. In this case the menu is named "Finder" and the item is "Preferences".
By deleting the file, you remove the corruption, the app (Finder) recreated a default plist the next time it is run (for Finder, that typically means reboot unless you do some command line work). New plist is clean, you can reset the preferences, Finder is ok until it happens again.
I posted my solution because it was the third time it had happened to me last year and figured others were having the same issue, and the same frustration with "google it" style answers ;-)
But before you go looking for an app that helps you detect corrupt plists, know that I have never had any of them work due to how the plist is designed. It has been a manual (and regular) effort since the inception of Mac OS X. This is one of the system's Achilles heals.
