OK, I removed it from WSUS by "deleting" the server in the list of computers, rebooted, ran the update in question, and rebooted again. I figured that if the update required a reboot to install, I would give it every chance possible to install. Unfortunately, none of it worked and the update still shows as being needed. I guess I have some questions here...
Looking in Control Panel - Windows Updates - View Update History, it says that this update has installed sucessfully. Several times, in fact. Is this really the case, or is this just a file that remains in some "windows update install cache" that I can delete? Or is it really expecting me to download and install it? It doesn't seem to be downloading, because a 55 MB file would take longer to download before trying to install.
The CBS log says gives the exact same message as above, that the package is invalid and can't be opened, or some such thing. This leads me to believe that I should removed this update from the aforementioned "windows update install cache" (wherever that is) and delete that file. Then go out and request windows updates again and see if that file downloads. I would think that would cure a corrupt file download, which it seems is the case. Is that a fair assessment, and how would I go about doing that? Thanks in advance.