以前的的发送消息按钮事件改写如下：
'/////////////////////转到发送即时消息页面
    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Dim i, j As Integer
        j = 0
        Dim tostu_id As String = ""
        For i = 0 To mycheck.Items.Count - 1
            If mycheck.Items(i).Selected Then
                '////////////////////////限制发送条数
                j = j + 1
                If j < 6 Then
                    '/////////////////////参数构造
                    tostu_id = tostu_id & CheckBoxList1.Items(i).Text & ""
                Else
                    Label2.Visible = True
                    Label2.Text = "一次最多能给五个用户发送信息！"
                    Return
                    'Response.Write("<script language=JavaScript>window.open('info.aspx?tostu_id=' & CheckBoxList1.Items(i).Text,'','height=330,width=560,status=no,location=no,toolbar=no,directories=no,menubar=no')</script>")
                End If
            End If
        Next i
        Response.Redirect("info.aspx?tostu_id=" & tostu_id)
    End Sub



这里发送信息的页面由于修改的比较多，所以把全部代码全都抓来了，呵呵：）
codebebind部分：
Imports System.Data
Imports System.Data.SqlClient
Public Class info
    Inherits System.Web.UI.Page
    Protected WithEvents Label1 As System.Web.UI.WebControls.Label
    Protected WithEvents Label2 As System.Web.UI.WebControls.Label
    Protected WithEvents TextBox2 As System.Web.UI.WebControls.TextBox
    Protected WithEvents Button1 As System.Web.UI.WebControls.Button
    Protected WithEvents Button2 As System.Web.UI.WebControls.Button
    Protected WithEvents Label3 As System.Web.UI.WebControls.Label
    Protected WithEvents Label4 As System.Web.UI.WebControls.Label
    Protected WithEvents Label5 As System.Web.UI.WebControls.Label
    Protected WithEvents Label6 As System.Web.UI.WebControls.Label
            Protected WithEvents TextBox3 As System.Web.UI.WebControls.TextBox
    Protected WithEvents Image3 As System.Web.UI.WebControls.Image
    Protected WithEvents Label8 As System.Web.UI.WebControls.Label
    Protected WithEvents Label7 As System.Web.UI.WebControls.Label
    Protected WithEvents Label9 As System.Web.UI.WebControls.Label
    Protected WithEvents Label10 As System.Web.UI.WebControls.Label
    Protected WithEvents Button3 As System.Web.UI.WebControls.Button
    Protected WithEvents Label11 As System.Web.UI.WebControls.Label
            Protected WithEvents TextBox1 As System.Web.UI.WebControls.TextBox

#Region " Web Form Designer Generated Code "

    'This call is required by the Web Form Designer.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

    End Sub

    Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
        'CODEGEN: This method call is required by the Web Form Designer
        'Do not modify it using the code editor.
        InitializeComponent()
    End Sub

#End Region
    Dim conn As SqlConnection = New SqlConnection("server=lixinri;uid=sa;pwd=;database=99re1")
    Public Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If Not IsPostBack Then
            Dim tostu_id As String = Request.QueryString("tostu_id")
            Dim splitname() As String
'///////////这里用了Split函数将传过来的参数取出
            splitname = Split(tostu_id, "")
            If tostu_id = "" Then
                '//////////////////当回复留言时
                Dim sql As String = "select a.*,b.nick from info a,pwd b where a.fromstu_id=b.stu_id and a.tostu_id='" & Session("stu_id") & "' and a.term=1"
                Dim comm As SqlCommand = New SqlCommand(sql, conn)
                Dim dr As SqlDataReader
                conn.Open()
                dr = comm.ExecuteReader
                While dr.Read
                    Label3.Text = dr.Item("nick")
                    Label4.Text = dr.Item("tim")
                    Label5.Text = "    " & dr.Item("content")
                    TextBox1.Text = dr.Item("nick")
                    TextBox3.Text = dr.Item("fromstu_id")
                    TextBox1.Enabled = False
                    Label8.Visible = False
                    Label11.Visible = False
                End While
                dr.Close()
                comm.Cancel()
                '//////////////////////更新留言使留言属性为已阅读过
                Dim sql_1 As String = "update info set term=0 where tostu_id='" & Session("stu_id") & "' and term=1 and tim='" & Label4.Text & "'"
                comm = New SqlCommand(sql_1, conn)
                comm.ExecuteNonQuery()
            Else
                '////////////////////当发送留言时
                '/////////////////读取参数
                Dim i As Integer
                For i = 0 To UBound(splitname) - 1
                    Dim mysql As String = "select nick from pwd where stu_id='" & splitname(i) & "'"
                    Dim comm As SqlCommand = New SqlCommand(mysql, conn)
                    Dim dr As SqlDataReader
                    If i = 0 Then
                        conn.Open()
                        dr = comm.ExecuteReader
                        If dr.Read Then
                            TextBox1.Text = Trim(dr.item("nick")) & ";"
                        End If
                        control()
                        dr.close()
                    Else
                        dr = comm.ExecuteReader
                        If dr.Read Then
                            TextBox1.Text = TextBox1.Text & Trim(dr.item("nick")) & ";"
                        End If
                        control()
                        dr.close()
                    End If
                Next i
            End If
        End If
    End Sub
     '/////////////////control事件，没有什么实际意义，使代码简单罢了。
    Sub control()
        TextBox1.Enabled = False : Label3.Text = "" : Label4.Text = "" : Label5.Visible = False
        Label8.Visible = True : Label6.Visible = False : Label7.Visible = False : Label9.Visible = False
        Button3.Visible = False : Label11.Visible = True
        Label11.Text = "<a language=javascript>alert('发送成功！')</script>")
    End Sub

    '////////////////////返回继续发送
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Response.Redirect("boaman.aspx")
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        Response.Write("<script language=javascript>window.close()</script>")
    End Sub
End Class


感谢laodeng了：）