foldersTree 问题 左边栏不能收起来

Question

foldersTree = gFldr('<DIV CLASS=fldrroot><b>系统功能列表</b></DIV>','');

Class1 = insFldr(foldersTree, gFldr('<DIV CLASS=fldrroot>负责电梯信息</DIV>', ''));
insDoc(Class1, gLnk(1, '<a href=1dianti_list.php target=main>本人负责电梯信息</a>', '', 'images/editinfo.gif'));

Class2 = insFldr(foldersTree, gFldr('<DIV CLASS=fldrroot>电梯保养记录</DIV>', ''));
insDoc(Class2, gLnk(1, '<a href=baoyang_add.php target=main>添加电梯保养记录</a>', '', 'images/editinfo.gif'));
insDoc(Class2, gLnk(1, '<a href=1baoyang_list.php target=main>查询电梯保养记录</a>', '', 'images/editinfo.gif'));

Class3 = insFldr(foldersTree, gFldr('<DIV CLASS=fldrroot>个人信息修改</DIV>', ''));
insDoc(Class3, gLnk(1, '<a href=editrypassword.php target=main>修改密码</a>', '', 'images/editinfo.gif'));

insDoc(foldersTree, gLnk(1, '退出', 'logout.php', 'images/exit.GIF'));
initializeDocument(0);

点击那个减号不能将下面的子类收起来，这是什么问题啊？求解决