Linking error in mixed code

Hi all,
I have a .NET application which needs to use some Win APIs. I set the
linker option (of VC++ .NET 2008 Express) to '\clr' to use mixed code
and added the following line of code:

....
#pragma unmanaged
namespace UnManagedFuncs
{
    using namespace System::Runtime::InteropServices;

    [DllImport("user32", EntryPoint = "SetClipboardViewer", CharSet =
CharSet::Unicode)]
    extern "C" long __cdecl SetClipboardViewer(void* hWnd);

    [DllImport("user32", EntryPoint = "SetWindowLong", CharSet =
CharSet::Unicode)]
    extern "C" long __cdecl SetWindowLongW(void* hWnd, int nIndex, long
dwNewLong);

    [DllImport("user32", EntryPoint = "CallWindowProc", CharSet =
CharSet::Unicode)]
    extern "C" long __cdecl CallWindowProcW(long* lpPrevWndFunc, void*
hWnd, unsigned int uMsg, unsigned int wParam, long lParam );

....
}

#pragma managed
namespace MyApp
{
                  ...
                  private: System::Void frmMain_Load(System::Object^
sender, System::EventArgs^ e)
    {
                  // Register this window to receive 'clipboard contents
changed' event
        UnManagedFuncs::SetClipboardViewer((void*)this->Handle);

                                UnManagedFuncs::HookWindow((void*)this-


                }
}

I get the following linker errors:
ScratchBook.obj : error LNK2019: unresolved external symbol
_CallWindowProcW referenced in function _UnManagedWinProc
ScratchBook.obj : error LNK2019: unresolved external symbol
_SetWindowLongW referenced in function "void __cdecl
UnManagedFuncs::HookWindow(void *)" (?
HookWindow@UnManagedFuncs@@YAXPAX@Z)

What is wrong?