Three20 crash when using PhotoSource

In my app I send a request to get images from flickr. I have went through my app step-by-step with a breakpoint and found the app crashes at this line in TTURLRequest.m:

} else { 

    return [self.urlPath md5Hash]; 
  } 

I get this error开发者_高级运维 in the debugger:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSCFString md5Hash]: unrecognized selector sent to instance 0x74409e0'

Does anybody know what is causing this? Thanks

check your "other linker flag" settings. This could happen if you have not set your "other linker flags" properly. It has to be -ObjC and -all_load. any mistake in uppercase or lowercase will also cause this problem