Hello I am currently working on an IOS app in xcode 6. I am getting the following error when archiving the application. It runs successfully when built on the emulator. After further inspection I've found this specific error message while compiling each piece of code step-by-step in the terminal. 

```
    Undefined symbols for architecture armv7:
 "_OBJC_CLASS_$_FBAppCall", referenced from:
  objc-class-ref in AppDelegate.o
"_OBJC_CLASS_$_FBLoginView", referenced from:
  objc-class-ref in AppDelegate.o
"_OBJC_CLASS_$_FBProfilePictureView", referenced from:
     objc-class-ref in AppDelegate.o
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)

```