Software Update cant find the update srvr. Make sure youre connected to net

Since the last version of iTunes was released (this was when I noticed it not working anyway) I haven't been able to do updates. I can go to the menu and look for the software updates. It will search for them and tell me which ones I need. I can then choose the updates I want and download them and it will start downloading. It will get to 115mb of 115mb downloaded, say it's downloading and verifying, but then it says "Software Update can’t find the update server. Make sure you’re connected to the Internet, then try again.

It does this for any updates that are waiting. I am connected to the internet so I don't know why it won't connect to the download server. Can someone tell me why this is happening?

Thanks.