Private Sub Form_Load()
Dim conn As New ADODB.Connection
Dim connectionstring As String
connectionstring = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & ".\db1.mdb;Persist Security Info=False"
conn.Open connectionstring
End Sub
Private Sub Command1_Click()
Dim sql As String
Dim conn As New ADODB.Connection
Dim rs_login As New ADODB.Recordset
If Trim(Text1.Text) = "" Then               '检测用户名正确与否
    MsgBox "用户名不能为空，请重新输入！", vbOKOnly + vbExclamation, "错误"
    Text1.SetFocus
Else
    Set rs_login = New ADODB.Recordset
    Set conn = New ADODB.Connection
    conn.Open "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & ".\db1.mdb;Persist Security Info=False"
    sql = "select * from LOGIN where USERID  = '" & Text1.Text & "'"
    rs_login.Open sql, conn, 1, 1  ///至少有一个参数未被指定
    If rs_login.EOF = True Then
        MsgBox "用户名不存在，请重新输入！", vbOKOnly + vbExclamation, "错误"
        Text1 = ""
        Text2 = ""
        Text1.SetFocus
    Else                                        '检测密码正确与否
        If Trim(rs_login.Fields(1)) = Trim(Text2) Then
           If Trim(rs_login.Fields(2)) = Trim(Combo1.Text) Then
           rs_login.Close
           Unload Me
           Form1.Show
           Else
           MsgBox "身份错误，请重新选择！", vbOKOnly + vbExclamation, "错误"
           Combo1.SetFocus
           End If
        Else
            MsgBox "密码错误，请重新输入！", vbOKOnly + vbExclamation, "错误"
            Text2 = ""
            Text2.SetFocus
        End If
    End If
End If
End Sub

运行后提示红色处至少有一个参数未被指定 ,新手初学，请大家帮忙调试一下 谢谢！！