php - forced zip file for download is corruption on unzip -

i have zip file. have made script force getting download

but issue that, when unzip saved zipped file, error stating :either file corrupt or

here's script

$itsfile = $folder.'.zip';  $file_name = basename($itsfile);  header("content-type: application/octet-stream"); header("content-disposition: attachment; filename=$file_name"); header("content-length: " . filesize($itsfile));  readfile($itsfile); exit; 

but still, when unziping saved file, getting error.

!   d:\documents , settings\administrator\desktop\file.zip: archive either in unknown format or damaged 

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edit: 

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the zip file contains foldr called image images inside it, , csv file havig data: information anyway?