Help! Error C2664 (cannot convert)

I'm trying to develop a very simple COM collection enumerator using ATL
(Visual Studio 2005 SP1). I want an object named ILibrary to return a
collection of IBook's. But I keep getting the same error in atlcom.h (line
211):

error C2664: '_CopyVariantFromInterface<T>::copy' : cannot convert parameter
2 from 'IBook *const *__w64 ' to 'IBook **'

I don't know if I should be casting or converting anything myself. Below is
the relevant code.

Here's the library class:

typedef vector<IBook*> BOOK_VECTOR;
typedef CComEnumOnSTL<CComIEnum<VARIANT>, &IID_IEnumVARIANT, VARIANT,
_CopyVariantFromInterface<IBook>, PERSON_VECTOR > VarEnum;

class ATL_NO_VTABLE CLibrary:
    public CComObjectRootEx<CComSingleThreadModel>,
    public CComCoClass<CLibrary, &CLSID_Employer>, public
ICollectionOnSTLImpl<IDispatchImpl<ILibrary, &IID_ILibrary, &LIBID_TestLib>,
                        BOOK_VECTOR, VARIANT, _CopyVariantFromInterface<IBook>, VarEnum>

Here's the copy policy class:

template < class T >
class _CopyVariantFromInterface
{
public:
    static HRESULT copy(VARIANT* pV, T** pIP)
    {
        HRESULT hr = (*pIP)->QueryInterface(IID_IDispatch, (void**)&pV->pdispVal);
        if(SUCCEEDED(hr) )
            pV->vt = VT_DISPATCH;
        else
        {
            (*pIP)->AddRef();
            pV->vt = VT_UNKNOWN;
            pV->punkVal = (*pIP);
        }
        return S_OK;
    }

    static void init(VARIANT* p) { VariantInit(p); }
    static void destroy(VARIANT* p) { VariantClear(p); }
};

Please help!
Thanks.