使用Microsoft.Office.Interop.Word向word文档中插入图形,发生错误[System.InvalidCastException]

使用Microsoft.Office.Interop.Word向word文档中插入图形,并且修改图形形态时,在执行到
object a = shape.Adjustments.Count;这句话时发生错误[System.InvalidCastException]环境windows 2003
office 2003使用dllPIA--->Office.dll  Version 11.0.0.0PIA--->Microsoft.Office.Interop.Word  Version 11.0.0.0
详细代码如下
try
            {
                object missing = System.Reflection.Missing.Value;
                Word.Application WordApp = new Word.Application();
                WordApp.Visible = true;
                
                Word.Document WordDoc = new Word.Document();
                Word.Selection se;
                WordDoc = WordApp.Documents.Add(ref missing, ref missing, ref missing, ref missing);
                
                 
                Word.Shape shape = WordDoc.Shapes.AddShape(30
                                                            , 100f
                                                            , 100f
                                                            , 200f
                                                            , 100f
                                                            ,ref missing);
                se = WordApp.Selection;
                shape.Select(ref missing);
                shape.Width = 400;
                
                object a = shape.Adjustments.Count;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }