Software Update not working

On my Mac Mini Software Update is not working as expected. I have this machine setup with multiple accounts and my kids accounts are very limited so they can use the computer safly while I am not home. My account has admin permissions. When I log into the computer and run Software Update it finds many (11) updates. I click install all and go do something else. I come back about 20 mintues later and found the system sitting at the "login" screen. I thought great it finished. Then I thought that was way to fast. So I log in and run Software Update again. You guessed it the same 11 items need an Update. So now I try and update them one at a time. I successfully updated a few items. Then I thought let me update the 4 items that require a reboot at one time. I started the update and left the machine alone for a while. I came back to the system saying I needed to restart. I clicked on OK. The system then said that it couldn't log out because "Software Update" was running. I could not do anything at this point except hold the power button in until the system powered down and I could then restart it.

To me it seams like a problem with the multi-user setup. Does anyone have any thoughts?

Thanks,
Scott