Problem with SoftwareUpdate

I'm trying to help out a friend that has an iMac. He's running 10.4.11. Whenever he tries to run Software Update, it downloads the update but when it tries to install the update it crashes SoftwareUpdate. The crash report complains about a kernel protection error but the console log says "can't load public key file".

I can download the updates and apply them successfully but SoftwareUpdate fails every time. I've got him current (all 32 updates) but I'd like to get this back in automatic update mode.

Anyone have a fix for this or pointers to a resolution?

Thanks, Bill