Windows SDK: using CallWindowProc()

Hi;

I am a beginning programmer a few months out of school.
I have been trying to become a windows programmer and have been studying Charels Petzold's
"PROGRAMMING WINDOWS95"

I have had trouble compiling some of his sample code that requires the SDK function
CallWindowProc().

The compiler tells me that the datatype for the first argument is wrong.  I checked the help
files and it isn't.  Changing the data type hasn't helped.

I don't know about size restrictions on posts here so I am not posting the whole program.
I can if someone wants me to.

I am listing the error message, the declaration of the first argument, the initialization of the
first argument, and the function call:

/*
***********************************************************
**        THE ERROR MESSAGE
***********************************************************
*/
C:\Program Files\DevStudio\MyProjects\W 25 Colors1\WinMain25.cpp(394) :
 error C2664: 'CallWindowProcA' : cannot convert parameter 1 from
 'long (__stdcall *)(void *,unsigned int,unsigned int,long)' to 'int (__stdcall *)(void)'

//Declaration of first argument
WNDPROC fnOldScr[3] ;
.
.
// Initialization Of First Argument
fnOldScr[i] = (WNDPROC) SetWindowLong( hwndScrol[i],   GWL_WNDPROC, (LONG) ScrollProc);

// The function call
return CallWindowProc( fnOldScr[i], hwnd, iMsg, wParam, lParam) ;