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

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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