Error when running on iOS 6 but not iOS 7

Question

I am trying to run my project on iOS 6 and I have set all the appropriate build settings to let me do so, but when I run on iOS 6 I get this error:

dyld: Symbol not found: _OBJC_CLASS_$_NSURLSession
  Referenced from: /var/mobile/Applications/8AC09960-A403-413E-B70A-E03DB2AF5844/Flywheel.app/Flywheel
  Expected in: /System/Library/Frameworks/Foundation.framework/Foundation
 in /var/mobile/Applications/8AC09960-A403-413E-B70A-E03DB2AF5844/Flywheel.app/Flywheel

What gives?? iOS 7 works fine.

Answer 1

The issue here is that the symbol isn't available on iOS 6. So you have to weak link the Foundation Framework by setting it's status to "optional" in Build Phases -> Link Binary With Libraries.