SCNetworkReachability compiling error
<p>I tried to compile Ercia Sadun's sample code <a href="http://github.com/erica/iphone-3.0-cookbook-/tree/master/C13-Networking/14-Web%20Browser/">here</a>, but this error came up:</p>

<pre><code>warning: in /Users/interdev/iphone source code/Web Browser/Classes/SystemConfiguration.framework/SystemConfiguration, missing required architecture i386 in file
    Undefined symbols:
      "_SCNetworkReachabilityScheduleWithRunLoop", referenced from:
          +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
      "_SCNetworkReachabilityCreateWithAddress", referenced from:
          +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
          +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
      "_SCNetworkReachabilityUnscheduleFromRunLoop", referenced from:
          +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
      "_SCNetworkReachabilitySetCallback", referenced from:
          +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
          +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
          +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
      "_SCNetworkReachabilityGetFlags", referenced from:
          +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
          +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
    ld: symbol(s) not found
    collect2: ld returned 1 exit status
        "_SCNetworkReachabilityScheduleWithRunLoop", referenced from:
            +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
        "_SCNetworkReachabilityCreateWithAddress", referenced from:
            +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
        "_SCNetworkReachabilityUnscheduleFromRunLoop", referenced from:
            +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
        "_SCNetworkReachabilitySetCallback", referenced from:
            +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) scheduleReachabilityWatcher:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) unscheduleReachabilityWatcher] in UIDevice-Reachability.o
        "_SCNetworkReachabilityGetFlags", referenced from:
            +[UIDevice(Reachability) hostAvailable:] in UIDevice-Reachability.o
            +[UIDevice(Reachability) pingReachabilityInternal] in UIDevice-Reachability.o
      ld: symbol(s) not found
      collect2: ld returned 1 exit status
    Build failed (5 errors)
</code></pre>

<p>...Even after I added systemConfiguration.framework, it reported the same error. Why did it do this, and how can I make it work?</p>
