Software Update Error and Application connectivity problems

Question

Hi. Hoping someone can help me with issues I've been having since we added a wireless access point to our network at home two weeks ago. I'm sharing a network with two pcs, a pc laptop and a ps3. All of which are working fine either using the wireless access point or ethernet through our router.
I have a macbook which is picking up the wireless fine, apart from a few applications. The biggest problem is that software update isn't connecting. I get a message telling me there is a networking error: NSURLError Domain - 1100. I go through the network diagnostics and it tells me that my connection is working correctly.
Another (less worrying but annoying) problem is that some widgets (facebook, wikipedia, translater etc) are not picking up the connection either. Facebook iphoto exporter also doesn't work. There is no in-built firewall in the access point and I haven't changed any firewall settings on my system (which was working perfectly with the ethernet connection). All I changed was the DNS server address.
The only time I have used airport previously is in the library at my university, where I needed to use a proxy address. I'm wondering if this may be interfering with my connection settings now, but am unsure of how to change the setting around. I'm a new mac user and this is the first issue I've had issues. Any help/suggestions are thoroughly appreciated.
thanks.

Answer 1

I'd been having this problem for the past few weeks (causing Software Update to fail with NSURLError -100 and the iTunes radio service to fail) and just fixed it myself.
For me the issue had to do with proxy settings in the browser versus proxy settings in System Preferences. For example, if you run Tor/Vidalia with Firefox, the browser has its own proxy settings that get changed when you activate Tor. But if you use Safari or anything else to set up the proxy, it's the network settings under System Preferences that get affected.
To check this, go to (Apple menu)>System Preferences...>Network, then choose whichever network interface you're currently using. If the lock icon in the lower left-hand corner is locked, click on it and authenticate with your password. Now click Configure... and choose the Proxies tab.
On my machine, I have "Configure proxies:" set to "Manually" (I've never used the other option, "Using a PAC file", so if you have that set I'm not sure how to debug it). Now look through the items in the "Select a proxy server to configure" panel. If there is anything checked there, it should be for a specific reason. If something is checked and you don't know why, try unchecking it.
Finally, click on Apply Now (giving your password again if prompted), close the System Preferences dialog, and try Software Update again.
This solved my problems (I had been fiddling with a local proxy for OS X Mail and Thunderbird). Your mileage may vary. Give that a shot and report back if it helps (or if it doesn't).
/HJ