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 href=board.aspx><<<返回学友录</a>"
   End Sub
  
   '/////////////////书写提交消息事件
   Public Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
   Dim tostu_id As String = Request.QueryString("tostu_id")
   Dim splitname() As String
   splitname = Split(tostu_id, "@")
   If tostu_id = "" Then
   '/////////////////////////当回复留言时
   If TextBox2.Text = "" Or TextBox2.Text = " " Then
   Label10.Visible = True
   Label10.Text = "消息不能为空！"
   Return
   Else
   Label10.Visible = False
   conn.Open()
   Dim sql As String = "insert into info(fromstu_id,tostu_id,content,term,tim) values(@fromstu_id,@tostu_id,@content,@term,@tim)"
   Dim comm As SqlCommand = New SqlCommand(sql, conn)
   comm.Parameters.Add(New SqlParameter("@fromstu_id", SqlDbType.Int, 4))
   comm.Parameters("@fromstu_id").Value = Session("stu_id")
  
   comm.Parameters.Add(New SqlParameter("@tostu_id", SqlDbType.Int, 4))
   comm.Parameters("@tostu_id").Value = TextBox3.Text
  
   comm.Parameters.Add(New SqlParameter("@content", SqlDbType.VarChar, 200))
   comm.Parameters("@content").Value = TextBox2.Text
  
   comm.Parameters.Add(New SqlParameter("@term", SqlDbType.Int, 4))
   comm.Parameters("@term").Value = "1"
  
   comm.Parameters.Add(New SqlParameter("@tim", SqlDbType.Char, 20))
   comm.Parameters("@tim").Value = Date.Now
   comm.ExecuteNonQuery()
   'TextBox2.Text = ""
   End If
   Else
   '/////////////////////////当发送留言时
   If TextBox2.Text = "" Or TextBox2.Text = " " Then
   Label10.Visible = True
   Label10.Text = "消息不能为空！"
   Return
   Else
   '////////////////插入i条数据
   Dim i As Integer
   For i = 0 To UBound(splitname) - 1
   Label10.Visible = False
   If i = 0 Then
   conn.Open()
   Else
   End If
   Dim sql As String = "insert into info(fromstu_id,tostu_id,content,term,tim) values(@fromstu_id,@tostu_id,@content,@term,@tim)"
   Dim comm As SqlCommand = New SqlCommand(sql, conn)
   comm.Parameters.Add(New SqlParameter("@fromstu_id", SqlDbType.Int, 4))
   comm.Parameters("@fromstu_id").Value = Session("stu_id")
  
   comm.Parameters.Add(New SqlParameter("@tostu_id", SqlDbType.Int, 4))
   comm.Parameters("@tostu_id").Value = splitname(i)
  
   comm.Parameters.Add(New SqlParameter("@content", SqlDbType.VarChar, 200))
   comm.Parameters("@content").Value = TextBox2.Text
  
   comm.Parameters.Add(New SqlParameter("@term", SqlDbType.Int, 4))
   comm.Parameters("@term").Value = "1"
  
   comm.Parameters.Add(New SqlParameter("@tim", SqlDbType.Char, 20))
   comm.Parameters("@tim").Value = Date.Now
   comm.ExecuteNonQuery()
   'TextBox2.Text = ""
   Next i
   End If
   End If
   Response.Write("<script 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：）