this.form1为空或不是对象???

  <div align="center">
                <input type="submit" name="Submit" value="删除所选"  class="go-wenbenkuang">
                全选
                <input type="checkbox" name="checkbox" value="Check All" onClick="mm()">
                &nbsp;&nbsp;
                <input type="submit" name="Submit2" value="排序"  onClick="form1.action='editnews.asp?action=px'">
              &nbsp;&nbsp; </div>

  <div align="center">
                <input type="submit" name="Submit" value="删除所选"  class="go-wenbenkuang">
                全选
                <input type="checkbox" name="checkbox" value="Check All" onClick="mm()">
                &nbsp;&nbsp;
                <input type="submit" name="Submit2" value="排序"  onClick="this.form1.action='editnews.asp?action=px'">
              &nbsp;&nbsp; </div>

底下的代码就会报错：this.form1为空或不是对象???

奇怪的问题！原因呢？