Only variables should be passed by reference

// Other variables $MAX_FILENAME_LENGTH = 260; $file_name = $_FILES[$upload_name]['name']; //echo "testing-".$file_name."<br>"; //$file_name = strtolower($file_name); $file_extension = end(explode('.', $file_name)); //ERROR ON THIS LINE $uploadErrors = array( 0=>'There is no error, the file uploaded with success', 1=>'The uploaded file exceeds the upload max filesize allowed.', 2=>'The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form', 3=>'The uploaded file was only partially uploaded', 4=>'No file was uploaded', 6=>'Missing a temporary folder' ); Any ideas? After 2 days still stuck.