App work on iOS4 but crash on iOS3.x

1. iPhone Configuration Utility to look at the console
2. if crash, crash report will be generated
3. use XCode Orgainizer > Device Logs to view the crash report
4. it said

Dyld Error Message:
  Symbol not found: __NSConcreteStackBlock
  Referenced from: /var/mobile/Applications/192B30ED-16AC-431E-B0E9-67C1F41FD5DA/MyApp.app/MyApp
  Expected in: /usr/lib/libSystem.B.dylib
  Dyld Version: 149

5. solution from forum:
 if you use blocks anywhere in your application, you'll see a crash similar to this on a pre-4.0 OS while building with the LLVM compiler. To work around this, you can specify the linker flag -weak-lSystem in your Xcode build settings.




Points to note:
1. Titanium bulit project file (.xcodeproj) can be compiled and run by XCode 4.0 connecting to iOS 4 device. If connecting to iOS3.x, need to install "iOS3.0-3.2.2 Device Debugging Support". You will be prompted to install this component when trying to run xcode project on device of iOS3.x


2. Titanium bulit project file (.xcodeproj) can't be compiled and run by XCode3.2.5 without existence of Titanium SDK. 
Install Titanium Studio and try again (TBC)


3.