activeX中GetBoundingBox的怪问题

prodevelop

用VC++7,VC++8开发activex方式AutoCAD想获得IAcadBlockReference 的 大小，碰到一个怪问题：

来操作AutoCAD2004的时候，一切正常，来操作AutoCAD2007的时候，却得不到结果：代码如下：

void GetBlockWidthAndHeight(double* width, double* height, AutoCAD::IAcadBlockReference *pblkRef)
{
    VARIANT minPoint, maxPoint;
    double* pMaxData = NULL,* pMinData = NULL;
    HRESULT hr;
    SAFEARRAYBOUND minBound[1], maxBound[1];

    VariantInit(&minPoint);
 VariantInit(&maxPoint);

    minBound[0].lLbound = 0;
    minBound[0].cElements = 3;
    maxBound[0].lLbound = 0;
    maxBound[0].cElements = 3;

    minPoint.vt = VT_ARRAY | VT_R8;
    maxPoint.vt = VT_ARRAY | VT_R8;
    minPoint.parray = SafeArrayCreate(VT_R8, 1, minBound);
    maxPoint.parray = SafeArrayCreate(VT_R8, 1, maxBound);

 hr = pblkRef->GetBoundingBox(&minPoint, &maxPoint);
 hr = SafeArrayAccessData(minPoint.parray, (void**)&pMinData);
    hr = SafeArrayAccessData(maxPoint.parray, (void**)&pMaxData);

    *width = pMaxData[0] - pMinData[0];
    *height = pMaxData[1] - pMinData[1];

 hr = SafeArrayUnaccessData(minPoint.parray);
    hr = SafeArrayUnaccessData(maxPoint.parray);
}

操作AutoCAD2007的时候，hr = pblkRef->GetBoundingBox(&minPoint, &maxPoint); 之后，minPoint和maxPoint均变成：VT_EMPTY了，请帮忙看看什么原因