新手求助,连接正确,语句应该也没问题,不能进行删除操作!

Dim str As String
        Dim r = MsgBox("确定要删除吗？", MsgBoxStyle.YesNoCancel, "")
        If r = vbOK Then
            str = "delete from salesorder where 订单编号='" & ComboBox2.Text.Trim() & " '"
            sqlcon.Open()
            Dim sqlcmd As New System.Data.SqlClient.SqlCommand
            sqlcmd.Connection = sqlcon
             = str
            sqlcmd.ExecuteNonQuery()
            MsgBox("删除成功！", MsgBoxStyle.OkOnly)
            sqlcon.Close()
            str = ""
        Else
            MsgBox("删除失败！", MsgBoxStyle.OkOnly)
        End If
登陆时使用相同连接来查询用户名及密码,所以连接应该不会错,与config文件中一样!
已经用了三种方法,不能实现删除!
sa 空密码,表权限正常,求助高手