Invalid argument foreach #24

When trying to upload a file i get the following error:

Warning (2): Invalid argument supplied for foreach() [APP/Plugin/file_upload/Controller/Component/FileUploadComponent.php, line 341]

The lines are:

function processAllFiles(){
foreach($this->uploadedFiles as $file){
$this->_setCurrentFile($file);
$this->Uploader->file = $this->options['fileModel'] ? $file[$this->options['fileVar']] : $file;
$this->processFile();
}
}

How to i solve this? Thanks.