Valgrind says invalid entry, but I just assign the line

I've been doing this for half a day, and I can't figure out why Valgrind is unhappy.

Valgrind whines:

==25658== Invalid write of size 4
==25658==    at 0x40242F: MyObject::copy(MyObject const&) (MyObject.cpp:96)
==25658==    by 0x402264: MyObject::operator=(MyObject const&) (MyObject.cpp:40)

      

        
        
        
      

    

MyObject.cpp: 96 is in my copy function

 94 void MyObject::copy(const MyObject & other)
 95 {
 96         myVariable = other.myVariable;

      

        
        
        
      

    

MyObject.cpp: 40 is in the assignment statement

 36 MyObject & MyObject::operator=(const MyObject & other)
 37 {
 38         if (this != &other)
 39         {
 40                 copy(other);
 41         }
 42         return *this; 
 43 }

      

        
        
        
      

    

MyVariable is of type String

 17 class MyObject
 18 {
 19         public:
 20 
 21         /** My Variable */
 22         string myVariable;

      

        
        
        
      

    

I see no reason why Valgrind would find a problem with this code. What am I missing?