Mac OS X 10.6.3 (Originally installed w/ English, later changed to Japanese)
Using Mac’s Software Update system, I was presented w/ the above error followed by “Some of the selected updates couldn’t be installed, an unexpected exception occurred.” Deleting the contents /Library/Update did not help. My system was running in Japanese mode.
Change the system back to English, run Software Update again. Success.
No clue as to why I had to do this, I thought all underlying binaries were written in the same language, but I guess I might be mistaken.