调用dll，结果窗体不见了，被释放了？

form2.paraent=form1，在form2里我调用了如下的dll，不知道为什么每次调用完了之后窗体就不见了，有时候甚至直接被关闭，现象是：运行后，窗体不见，用鼠标点一下任务栏，窗体被最小化，再按恢复正常，请高手帮忙
unit Funwritecard;interface
function Write_Card(AHandle:THandle;Com:Cardinal;RPassword,WPassword,Password:Pchar; IsShow:Boolean):Boolean;stdcall;
type
  TWrite_Card = Function(AHandle:THandle;Com:Cardinal;RPassword,WPassword,Password:Pchar; IsShow:Boolean):Boolean;stdcall;// ;RPassword,WPassword,Password:Pchar
implementation
uses
  Windows,
  SysUtils,
  Classes ,
  Dialogs,
  Messages,
  Controls,
  Forms,
  UniwsCardInt,
  publicfunction;
var
  pTWriteCard:TWrite_Card;
  LibHandle:THandle;
function Write_Card(AHandle:THandle;Com:Cardinal;RPassword,WPassword,Password:Pchar; IsShow:Boolean):Boolean;stdcall;
var
  FileName:String;
begin
  result:=false;
  if LibHandle<>0 then
  FreeLibrary(LibHandle);
  FileName:=Getfilename();
  LibHandle:=LoadLibrary(Pchar(FileName));
  if LibHandle<>0 then
  begin
    try      @pTWriteCard:=GetProcAddress(LibHandle,'Write_Card');      if not (@pTWriteCard = nil) then
      begin
        result:=pTWriteCard(AHandle,Com,RPassword,WPassword,Password,IsShow);
      end;
    finally
      FreeLibrary(LibHandle);
    end;
  end
  else
     ShowMessage('装载动态库'+Pchar(FileName)+'失败！');
  end;
end.