iMac will no longer update via software update

[Europe calling]

Hi,

My dads iMac (G5, 2Ghz, OSX 10.4.10) will no longer update via software update. It has done this before without any issues.
It now pops out a message saying there is no network connection, which is odd because internet and mail just work fine.
What can cause this? And how can i resolve it?

 

[mad jew]

Is it the same error in all user accounts? Can you manually download the updates from Apple's site? What sort of network are you on?