“仅应通过引用传递变量”错误

我真的看不懂PHP，但我正在尝试通过php在我的页面中上传csv文件，并得到以下错误。我知道有很多线程在谈论这个，但我不太明白它们是什么意思。如果有人可以向我解释发生了什么并提供解决方案，请寻找答案。

严格的标准：只有变量应该通过引用传递 in C：''xampp''htdocs''search''php''loader''csvFileUploader1.php on 第 9 行上传
文件失败>>> 错误代码：
1

这是 PHP

<?php
// using upload at click from http://code.google.com/p/upload-at-click/
// FileData is the name for the input file
$file_result = "";
$file = $_FILES['Filedata'];
$allowedExtensions = array("csv", "txt");
$extension = end(explode(".", $file["name"]));

function isAllowedExtension($fileName) {
    global $allowedExtensions;
    return in_array(end(explode(".", $fileName)), $allowedExtensions);
}
if($file["error"] > 0){
    echo "failure to upload the file >>> ". "Error code: ".$file["error"]."<br>";
}else{
    //echo " >>> CURRENT DIR: ".getcwd() . "'n";
    $workDir = getcwd();
    $dir = substr($workDir, 0, -10);
    $path = $file["name"];
    $newFileLoc = $dir.$path;
    $file_result.=
    "<br>     Upload: " . $file["name"] . "<br>" .
    "     Type: " . $file["type"] . "<br>" .
    "     Size: " . $file["size"] . "<br>" .
    "     file uploaded to: ".$newFileLoc."<br>";
    // txt - text/plain
    // rtf - application/msword
    // dat/obj - application/octet-stream
    // csv - application/vnd.ms-excel
    // maximum 200 MB file - 200,000,000 k
    if (    ($file["type"] == "application/vnd.ms-excel" || $file["type"] == "text/plain")
            && isAllowedExtension($file["name"])
            && ($file["size"] < 200000000)
        )
        {   
            move_uploaded_file($file["tmp_name"], $newFileLoc);
            //echo $file_result.=" >>> File uploaded successfull!!";
            echo "|".$path;//"filePath : " . $newFileLoc;
        }else{
            echo " >>> NOT a file valid: ". isAllowedExtension($file["name"]);
        }       
}

?>