Problem reading from a file on a share

unit FileMapping;
 
 
interface
 
uses
  Windows;
 
type
  TFileMap = class(TObject)
  private
    FFileName : String;
    FileHandle : THandle;
    MapHandle : THandle;
    FBOFPtr : Pointer;
    FEOFPtr : Pointer;
    FFileSize : DWord;
  public
    constructor Create(FileName : String);
    destructor Destroy; override;
    procedure CreateFile(Size : DWord); overload;
    procedure CreateFile(FileName : String; Size : DWord); overload;
    procedure Open; overload;
    procedure Open(FileName : String); overload;
    procedure Close;
    function FilePtr(Ofs : DWord) : Pointer;
    property BOF : Pointer read FBOFPtr;
    property EOF : Pointer read FEOFPtr;
    property FileSize : DWord read FFileSize;
    property FileName : String read FFileName write FFileName;
  end;
 
implementation
 
{ TFileMap }
 
uses
  SysUtils,
  Dialogs;
 
constructor TFileMap.Create(FileName: String);
begin
  inherited Create;
 
  FFileSize:=0;
  FBOFPtr:=NIL;
  FEOFPtr:=NIL;
  MapHandle:=0;
  FileHandle:=INVALID_HANDLE_VALUE;
 
  Open(FileName);
end;
 
destructor TFileMap.Destroy;
begin
  Close;
  inherited;
end;
 
procedure TFileMap.CreateFile(Size: DWord);
begin
  Close;
 
  FileHandle:=Windows.CreateFile(PChar(FFileName),
                         GENERIC_READ or GENERIC_WRITE,
                         FILE_SHARE_READ or FILE_SHARE_WRITE,
                         NIL,
                         OPEN_ALWAYS,
                         FILE_ATTRIBUTE_NORMAL,
                         0);
  if FileHandle<>INVALID_HANDLE_VALUE then
    MapHandle:=CreateFileMapping(FileHandle,
                                 NIL,
                                 PAGE_READWRITE,
                                 0, Size,NIL);
  if MapHandle<>0 then
    FBOFPtr:=MapViewOfFile(MapHandle, FILE_MAP_ALL_ACCESS,0,0,Size);
 
  if FBOFPtr<>NIL then begin
    FFileSize:=Size;
    FEOFPtr:=POINTER(DWORD(FBOFPtr)+FFileSize);
  end else begin
    ShowMessage(Format('Error %d. "%s"',[GetLastError,SysErrorMessage(GetLastError)]));
    Close;
  end;
 
end;
 
procedure TFileMap.CreateFile(FileName: String; Size: DWord);
begin
  if FileName<>'' then begin
    FFileName:=FileName;
    CreateFile(Size);
  end;
end;
 
procedure TFileMap.Open;
begin
  Close;
 
  FileHandle:=Windows.CreateFile(PChar(FFileName),
                         GENERIC_READ or GENERIC_WRITE,
                         FILE_SHARE_READ or FILE_SHARE_WRITE,
                         NIL,
                         OPEN_EXISTING,
                         FILE_ATTRIBUTE_NORMAL or FILE_FLAG_SEQUENTIAL_SCAN,
                         0);
  if FileHandle<>INVALID_HANDLE_VALUE then
    MapHandle:=CreateFileMapping(FileHandle,
                                 NIL,
                                 PAGE_READWRITE,
                                 0,0,NIL);
  if MapHandle<>INVALID_HANDLE_VALUE then
    FBOFPtr:=MapViewOfFile(MapHandle, FILE_MAP_ALL_ACCESS,0,0,0);
 
  if FBOFPtr<>NIL then begin
    FFileSize:=GetFileSize(FileHandle, NIL);
    FEOFPtr:=POINTER(DWORD(FBOFPtr)+FFileSize);
  end else begin
    Close;
  end;
end;
 
procedure TFileMap.Open(FileName: String);
begin
  if FileName<>'' then begin
    FFileName:=FileName;
    Open;
  end;
end;
 
procedure TFileMap.Close;
begin
  FFileSize:=0;
  if FBOFPtr<>NIL then begin
    FlushViewOfFile(FBOFPtr, 0); // Flush to disk
    UnmapViewOfFile(FBOFPtr);    // Unmap the view
    FBOFPtr:=NIL;
    FEOFPtr:=NIL;
  end;
 
  if MapHandle<>0 then begin
    CloseHandle(MapHandle);
    MapHandle:=0;
  end;
 
  if FileHandle<>INVALID_HANDLE_VALUE then begin
    CloseHandle(FileHandle);
    FileHandle:=INVALID_HANDLE_VALUE;
  end;
end;
 
function TFileMap.FilePtr(Ofs: DWord): Pointer;
begin
  if (FBOFPtr<>NIL) and (Ofs<FileSize) then
    Result:=POINTER(DWORD(FBOFPtr)+Ofs)
  else
    Result:=NIL;
end;
 
end.

                                  

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