上传图片有时候会弹出"HTTP错误"?

Question

上传图片偶尔会提示"HTTP错误"
我是在一个页面,多个实例上传.大部数都可以正常上传,偶尔会有用户反映出现上述提示.我捕捉不到错误信息,不知道问题出在哪里.
JSP代码:

                <div class="upload">
                    <div class="container">
                      <div class="body">
                        <div class="col-md-12">
                          <div id="container5">
                            <input type="text" id="hkbzp_url" name="" value="图片地址(注:上传图片大小不能超过1M.)" readonly="readonly" class="inp_title js_content" style="width: 430px; float:left;" verify="no" maxlength="1000">
                            <p class="baseBtn" id="hkbzp" style="cursor:pointer;float:left; width:70px; text-align:center; line-height:24px; margin-left:10px; position:relative; overflow:hidden;">
                              上 传
                            </p>
                            <input type="hidden" id="hkbzp_img_url" name="hkbzp_img_url" value="" />
                          </div>
                        </div>
                      </div>
                    </div>
                </div>

main.js代码:

var Qiniu5 = new QiniuJsSDK();
var option5 ={
    runtimes: 'flash,html5,html4',
    //  runtimes: 'flash',
    browse_button: 'hkbzp',
    container: 'container5',
    max_file_size: '1MB',
    flash_swf_url: '/qiniu/js/plupload/Moxie.swf',
    dragdrop: true,
    chunk_size: '4mb',
    uptoken_url: uptoken_url,
    domain: domainUrl,
    get_new_uptoken: true,
    //unique_names: true,
    save_key: true,
    auto_start: true,
    init: {
        'FilesAdded': function(up, files) {
        },
        'BeforeUpload': function(up, file) {

        },
        'UploadProgress': function(up, file) {

        },
        'UploadComplete': function() {
            ///'#success'.show();
        },
        'FileUploaded': function(up, file, info) {
            var jsonData = eval("(" + info + ")");
            var fileUrl=domainUrl+jsonData.key;
            $("#hkbzp_img_url").val(fileUrl);
            $("#hkbzp_url").val(fileUrl);
            alert("上传成功!");
        },
        'Error': function(up, err, errTip) {
            alert(errTip);
        }
    }

uptoken代码:
public static String makeUptoken() throws Exception {

    String ACCESS_KEY =Setting.getQiniuAccessKey();
    String SECRET_KEY = Setting.getQiniuSecretKey();
    Mac mac = new Mac(ACCESS_KEY, SECRET_KEY);
    String bucketName = Setting.getQiniuBucket();
    PutPolicy putPolicy = new PutPolicy(bucketName);
    // 可以根据自己需要设置过期时间,sdk默认有设置，具体看源码
    //String key =getUUID()+"$(ext)";
    String key =getUUID()+".jpg";
    putPolicy.expires = 4600000;
    putPolicy.scope=bucketName;
    putPolicy.fsizeLimit=1*1024*1024;
    //putPolicy.saveKey= getUUID()+"$(ext)";
    putPolicy.saveKey= key;
    //putPolicy.saveKey=getUUID();
    //putPolicy.saveKey= DateUtil.formatter(new Date(), "yyyyMMddHHmmss")+"_$(fname)";
    putPolicy.insertOnly=1;//默认0

    //putPolicy.persistentOps="avthumb/flv/r/24/vcodec/libx264";
    //putPolicy.persistentNotifyUrl="http://fake.com/qiniu/notify";
    //putPolicy.mimeLimit="video/mp4;video/flv;video/swf";
    //putPolicy.returnUrl = "http://localhost:80/qndemo/QiNiuCallback.jsp";//如不设置returnUrl，则直接将returnBody的内容返回给客户端
    //putPolicy.returnBody = "{\"name\": $(fname),\"size\": \"$(fsize)\",\"w\": \"$(imageInfo.width)\",\"h\": \"$(imageInfo.height)\",\"hash\":$(etag)}";
    String uptoken = putPolicy.token(mac);
    return uptoken;
}