software update won't connect

When I read about the 10.7.4 update I went to software update and clicked on check for updates. I got a dialog saying:Failed to check for updates. There was a problem communicating with the web proxy server (HTTP).

I went to the Apple site and downloaded the 10.7.4 combo update and installed it in the hopes that it would replace whatever had suddenly messed up the software update function; no luck.

I have done cold restarts and repaired permissions but these steps haven't fixed the problem. All the other internet works as expected except that a widget, Maintidget, will no longer accept my system password or check for updates. Has something perhaps blocked a port used to check for updates that is different than that used by Mail and Firefox?

I may have to do my updates manually until Mountain Lion in the hopes it will repair whatever has been corrupted.