Some people are reporting a build error in SVN, with a couple of missing symbols (kSCPropNetProxiesProxyAutoConfigEnable and kSCPropNetProxiesProxyAutoConfigURLString) in Frameworks/AIUtilities\ Framework/Source/AISystemNetworkDefaults.m. We know about this, and there's nothing we can do about it — the declarations of these symbols were incorrect in the headers that came with Xcode before 2.2, and were fixed in that version.

So if you're having this error, it means your Xcode is out of date. Update to 2.2 release (one person was using a seed of 2.2) and then try it.