using Clipboard functions in a DLL

I try to write a function that Copy's the Active window to a Bitmap file. When I use this function in a program it work's fine. When put it in a DLL it don't work.
Help!!!!!

function CopyActiveScreenToFile(FName: PChar): Boolean;
var TmpBMP:TBitmap;
    Data: THandle;
    Palette: HPALETTE;
begin
  Result := False;
  Clipboard.Open;
  keybd_event(VK_SNAPSHOT, 0, 0, 0);
  TmpBMP := TBitmap.Create;
  try
    Data := GetClipboardData(CF_BITMAP);
    Palette := GetClipboardData(CF_PALETTE);
    TmpBMP.LoadFromClipBoardFormat(CF_BITMAP, Data, Palette);
    TmpBMP.SaveToFile(FName);
    if FileExists(FName) then
      Result := True
    else
      Result :=False;
  finally
    TmpBMP.Free;
  end;
  Clipboard.Close;
end;