Could be many things, we should start with this...
"Try Disk Utility
1. Insert the Mac OS X Tiger Install disc that came with your computer, then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
*Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.*
3. Click the First Aid tab.
4. Select your Mac OS X volume.
5. Click Repair. Disk Utility checks and repairs the disk."
Then try a Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes.
(Safe boot may stay on the gray radian for a long time, let it go, it's trying to repair the Hard Drive.)
The usual reason why updates fail or mess things up, is if Permissions are not fixed before & after every update, with a reboot... you may get a partial update when the installer finds it doesn't have Permissions to change one obscure little part of the OS, leaving you with a mix of OS versions.
Some people get away without Repairing Permissions for years, some for only days.
If Permissions are wrong before applying an update, you could get mixed OS versions, if Directory is the slightest messed up, who knows!
If many Permission are repaired, or any Directory errors are found, you may need to re-apply some the latest/biggest updates.
May even need to do an Archive and Install if you have room on the HD, but saves all your files and gives a new OS...
I only use Software Update to see what is needed, then get them for real via...
That way I can wait a week or so, check the forums for potential problems, and get Permissions & such in order before installing.
If all the above fails, then it appears to be time for a relatively painless Archive & Install, which gives you a new/old OS, but can preserve all your files, pics, music, settings, etc., as long as you have plenty of free disk space and no Disk corruption, and is relatively quick & painless...
Just be sure to select Preserve Users & Settings.
when I verified/repaired the permissions this is the log
Name : Macintosh HD
Type : Volume
Disk Identifier : disk1s2
Mount Point : /Volumes/Macintosh HD 1
File System : Mac OS Extended (Journaled)
Connection Bus : FireWire
Partition Type : Apple_HFS
Device Tree : fw/node@16cbfffe59f05a/sbp-2@3bc600/@0:2
Writable : Yes
Universal Unique Identifier : 31D5AD5C-D975-379A-A0A3-04A67DC982F2
Capacity : 111.5 GB (119,690,149,888 Bytes)
Free Space : 80.6 GB (86,590,377,984 Bytes)
Used : 30.8 GB (33,099,771,904 Bytes)
Number of Files : 592,367
Number of Folders : 130,182
Owners Enabled : Yes
Can Turn Owners Off : Yes
Can Repair Permissions : Yes
Can Be Verified : Yes
Can Be Repaired : Yes
Can Be Formatted : Yes
Bootable : Yes
Supports Journaling : Yes
Journaled : Yes
S.M.A.R.T. Status : Not Supported
Disk Number : 1
Partition Number : 2
I connected my MBP(Target Disk Mode) to my ibook using firewire to transfer files and repair the disc permissions with disc utility, I also used TechTools to check and repair what I could, I couldn't repair the disc this because i could not be unmounted, I was able to borrow a friends install disc to unmount and repair the disc on the MBP. I couldn't reinstall the software because the discs came with his macbook (the gray discs).