Cannot modify header information - headers already sent

[eluser]Sudz[/eluser]
[quote author="toopay" date="1304166589"]Post the line 489 of your exel helper.[/quote]


On all these lines same error error comes

486

Code:

header("Content-type: application/zip");

487

Code:

header("Content-Disposition: attachment; filename=$archive_file_name");

488

Code:

header("Pragma: no-cache");

489

Code:

header("Expires: 0");