请教......

<%@import namespace="system.data"%>
 <script runat="server">
 
sub page_load(ob as object,ev as eventargs)
if page.ispostback=false
 dim myarray() as string={"red","yellow","blue","white","green"}
lb.datasource=myarray
end if
page.databind()
end sub
 
</script>
<html>
<body>
 
<form   runat="server">
<asp:listbox id="lb" autopostback="true" runat="server"/>
<asp:label  text="<%#lb.selecteditem.text%>" runat="server"/>
</form>
</body>
</html>
报错:对象引用未设置实例..
找不出是哪的错