error after return from dll.

I have this code:
////////////////////////
#include "stdafx.h"
typedef UINT (CALLBACK* LPFNDLLFUNC1)(DWORD,UINT);

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)

{

HINSTANCE hDLL;               // Handle to DLL
LPFNDLLFUNC1 lpfnDllFunc1;    // Function pointer
DWORD dwParam1;
UINT  uParam2=0, uReturnVal=0;

hDLL = LoadLibrary("azza");
if (hDLL != NULL)
{
   lpfnDllFunc1 = (LPFNDLLFUNC1)GetProcAddress(hDLL,"test2");
   if (!lpfnDllFunc1)
   {
      // handle the error
      FreeLibrary(hDLL);
      MessageBox(0,"error","error",0);
   }
   else
   {
      // call the function
      uReturnVal = lpfnDllFunc1(dwParam1, uParam2);
   }
}
return 0;
}
//////////////////////////

which calls function test2 in azza.dll.
When I run the program, the function is executed, but after the execution of the function, I have the following error:


/////////////////
---------------------------
Microsoft Visual C++ Debug Library
---------------------------
Debug Error!

Program: ... Files\Microsoft Visual Studio\MyProjects\user\Debug\user.exe
Module:
File: i386\chkesp.c
Line: 42

The value of ESP was not properly saved across a function call.  This is usually a result of calling a function declared with one calling convention with a function pointer declared with a different calling convention.

(Press Retry to debug the application)
---------------------------
Afbreken   Opnieuw   Negeren  
---------------------------
/////////////////////

I'm new to c++. What does this error means, and how should I solve it ??