主题：[求助]显示问题

你的主窗口是个模式窗口吧？ 如果是的，这个修改一下：

Dim UserName As String = e.Form.Controls("UserName").Value
Dim cmd As New SQLCommand
Dim dt As DataTable
Dim dr As DataRow
cmd.C
If UserName = ""  Then
    Messagebox.show("请选择用户!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
    Return
End If
cmd.CommandText = "Select * From {Users} Where [Name] = '" & UserName & "'"
dt = cmd.ExecuteReader

'---------------------------------------------------
If dt.DataRows.Count = 0 Then
    Messagebox.show("此用户不存在!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
    Return
Else
    dr = dt.DataRows(0)
    If e.Form.Controls("PassWord").Value = dr("Password") Then
        _UserName = UserName
        _UserGroup = dr("Group")

        e.Form.BaseForm.Hide()
        e.Form.Close
        Forms("主窗口").open()
    Else
        Messagebox.show("密码错误!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
    End If
End If