我要在拷贝文件时用进度条控件显示拷贝进度该怎么做？

[lqlling]

我的拷贝程序如下：
procedure TForm1.Button1Click(Sender: TObject);
var
S,T: TFileStream; {文件流}
SourceFileName,DestFileName:String;{源文件和目的文件名}
IniFile:TIniFile;
FileName:string;
begin
SourceFileName:='\\fornet-177\update\demo.txt';
DestFileName:='d:\test.txt';
S:=TFileStream.Create(SourceFileName, fmOpenRead );
try
T:= TFileStream.Create(DestFileName,fmOpenWrite or fmCreate );

try
T.CopyFrom(S,S.Size);
T.Free;
showmessage('拷贝成功!');
except
showmessage('拷贝失败，请手工拷贝!');
end;
S.Free;
except
showmessage('拷贝失败，请手工拷贝!');
end;
end;

[bestluo]

我写的函数如下：
可以参考
Procedure CanCopyFile(FromFile,ToFile:String;ProgressBar:TProgressBar);
var
FFile,TFile:file of byte;
Buffer : array[0..4096] of char;
NumRead : integer;
FileLength : longint;
begin
AssignFile(FFile,FromFile);
reset(FFile);
AssignFile(TFile,ToFile);
rewrite(TFile);
FileLength:=FileSize(FFile);
With Progressbar do
begin
Min := 0;
Max := FileLength;
while FileLength > 0 do
begin
BlockRead(FFile,Buffer[0],SizeOf(Buffer),NumRead);
FileLength := FileLength - NumRead;
BlockWrite(TFile,Buffer[0],NumRead);
Position := Position + NumRead;
end;
CloseFile(FFile);
CloseFile(TFile);
end;
Progressbar.Visible :=false;
end;

[lqlling]

我也用过BlockRead(),BlockWrite(),用这个是可以显示进度，但是在我拷贝网络机子上的文件时就报io出错，拷贝本机就可以。报错如下：
Project Project1.exe raised exception class EInOutError with message
'File access denied'.Process stopped.Use Step or Run to continue.