主题：错加错，不知错在哪了？

Dim ss As winForm.combobox
ss=e.Form.Controls("combobox1")
Dim cm As new sqlcommand
Dim txt As String = ss.Value
Dim hb As DataTable
cm.commandtext="select distinct 户别 from {zh} where 户名=txt"
hb=cm.executereader()
e.sender.combolist=hb.getcomboliststring("户别")

这段代码错在哪了？烦请高手指点