为什么用suiback里的suiMessageDialog1.showmodal不行??

[tflb]

我在登陆窗体放了一个suiMessageDialog1控件,但suiMessageDialog1.showmodal不能用,一用就出如下提示
错误提示
Access violation at address 00522DC3 in module 'student.exe'.write of address 000000060.

但在别的窗体应用正常,并且在登陆窗体应用showmessage('输入错误，请重输！');正常;
登陆的button如下:请各位帮忙看一下,有用过suiback的同志请指点一下!谢谢
procedure Tf_login.BitBtn1Click(Sender: TObject);
var
flag:boolean;//pass signal

begin

flag:=false;
right:=combobox1.ItemIndex;
logname:=trim(edit1.Text);
password:=trim(edit2.Text) ;
datamodule1.ADOQ_yh .Open ;
datamodule1.ADOQ_yh.First;
while not datamodule1.ADOQ_yh.Eof do
begin
if (logname=trim(datamodule1.ADOQ_yh.Fields[0].AsString)) and (password=trim(datamodule1.ADOQ_yh.Fields[1].AsString))
and (right=datamodule1.ADOQ_yh.Fields[2].AsInteger) then
flag:=true;
datamodule1.ADOQ_yh.Next;
smd2.Free;
end;
if flag then
begin
F_main.Show;
datamodule1.adoq_dl.Open;
datamodule1.adoq_dl.AppendRecord([logname,right,datetimetostr(now)]);
datamodule1.adoq_dl.Close;
edit2.Text:='';
if right=0 then
begin
smd2.free;
f_main.Show ;
end;
if right=1 then
begin
f_main.Show;
end;
f_login.free;

end
else
// APPLICATION.MessageBox('请输入学号！','错误',mb_OK);
smd2.Caption := '系统提示';
smd2.Text:= '您输入的用户名或密码错误,请重新输入!';
smd2.ShowModal ;
edit2.SetFocus ;
exit;
// showmessage('输入错误，请重输！');

end;

[tflb]

smd2.ShowModal;报错!!

[kuan]

不一定是控件问题，你设个断点，看看在哪句上报错？