libXcodeDebuggerSupport.dylib is missing in iOS 4.2.1 development SDK

What I just did to solve this problem was:

cd /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2.1 (8C148)/Symbols

and created the symlink was missing:

ln -s ../../4.2\ \(8C134\)/Symbols/Developer/ Developer

It solves my problem.