For various reasons -- including user interruption as described in this article -- components of Mac OS X can be "stepped on" (erased or otherwise damaged) during the incremental update process (e.g. installing Mac OS X 10.4.9).
In order to remedy this issue, there are two options; one far simpler than the other:
Re-apply the current Mac OS X combination updater Try this first. It is perhaps the most consistently successful workaround for issues that materialize after an incremental Mac OS X update with good reason: re-installing the combo update can replace components that were … Read more