Error Code 3 When Linking to DLL versus Static LIbrary

I'm a VB developer by trade but am trying to make the move to C++.
There are still some things that mystify me. Below is a simplified
version of my code but it still produces the same result. If I run the
application with both the CStock and CTick classes included in my
assembly or compiled under a static library the application works
perfectly. If, however, I place those two classes in a DLL I get the
following error when I exit the application:

The program '[1408] MyApp.exe: Native' has exited with code 3 (0x3).

For the life of me I can't figure out why. Any clue for this newbie?

TICK.H

   #ifndef TICK_H
   #define TICK_H

   class CTick
   {
   public:
      CTick(void);
      CTick(const CTick &Other);
      ~CTick(void);
      CTick &operator=(const CTick &Other);
      float fClose;
   };

   #endif

TICK.CPP

   #include "Tick.h"

   CTick::CTick(void) : fClose(0.0f)
   {
   }

   CTick::CTick(const CTick &Other) : fClose(Other.fClose)
   {
   }

   CTick::~CTick(void)
   {
   }

   CTick &CTick::operator=(const CTick &Other)
   {
      fClose = Other.fClose;
      return *this;
   }

STOCK.H

   #ifndef STOCK_H
   #define STOCK_H

   #include <vector>
   #include <string>
   #include "Tick.h"

   using namespace std;

   class CStock
   {
   public:
      CStock(void);
      CStock(const CStock &Other);
      ~CStock(void);
      CStock &operator=(const CStock &Other);
      vector<CTick> Quotes;
      string szSymbol;
   };

   #endif

STOCK.CPP

   #include "Stock.h"

   CStock::CStock(void)
   {
   }

   CStock::CStock(const CStock &Other)
   {
      szSymbol= Other.szSymbol;
      Quotes = Other.Quotes;
   }

   CStock::~CStock(void)
   {
   }

   CStock &CStock::operator=(const CStock &Other)
   {
      szSymbol = Other.szSymbol;
      Quotes = Other.Quotes;
      return *this;
   }

MAIN.CPP

   #include "Stock.h"
   #include "Tick.h"

   int _tmain(int argc, _TCHAR* argv[])
   {
    CStock myStock;
    myStock.SetSymbol("ABC");

    CTick myTick;
    myTick.SetClose(1.0f);

    myStock.Quotes.push_back(myTick);

    return 0;
   }