Out-of-line definition error on a class but it is declared in the header file

Now this is a weird problem. I was coding two days ago and stopped and then continued just now. On my header file (Fruit.h) I added a method called animateGrow() like so:

Fruit.h:

class Fruit {
private:
   // Member variables here

public:
   // Other methods here
   void animateGrow( );
};

But when I try to add the same method in the CPP file, I get an Out-of-line definition of 'animateGrow' does not match any declaration in 'Fruit' error. It's declared in the header but Xcode does not seem to be able to find that method.

Fruit.cpp:

#include "SimpleAudioEngine.h"
#include "Fruit.h"
#include "Tree.h"

using namespace cocos2d;
using namespace CocosDenshion;

Fruit::Fruit( ) {
   // Constructor
}

// Getter Methods
// Setter Methods
// Other Methods

void Fruit::animateGrow( ) {
   // I get an error here when I type it.
}

Full Code: (links removed) (In the code, the Tree class exists and all other methods and functions are working fine except for the animateGrow() as it gives me the error)