Error when attempting to parse xhr response text in fineUploader

I bay this fine-uploader version 3.3.0 now, and integration all lib in my site i think uploads make working its ok, but no! i see error my javascript console:

[FineUploader] Sending upload request for 0

[FineUploader] xhr - server response received for 0

[FineUploader] responseText = 

and error firebug:

[FineUploader] Error when attempting to parse xhr response text (SyntaxError: JSON.parse: unexpected end of data)

at line error: jquery.fineuploader-3.3.0.min.js(line 148)

i use params:

$(document).ready(function () {
    $('#uploader').fineUploader({
    request: {
        endpoint: '/upload/'
      },
    classes: {
        success: 'alert alert-success',
        fail: 'alert alert-error'
         }, 
    text: {
        uploadButton: '<i class="icon-upload icon-white"></i> file target'
      },
       validation: {
      sizeLimit: 31457280 

      },             
    debug: true

    });
  });

if i am write sizeLimit: 10485760 - it all right ok working! file uploads to finish. If write sizelimit: 31457280 file not uploads to end, process break to 2 or 3%. Help me! where bug? Please help me somebody!

The following log message:

Error when attempting to parse xhr response text (SyntaxError: JSON.parse: unexpected end of data)

Generally indicates your server is not returning a valid JSON response. This is usually caused by an unexpected error server-side. Note that you must ALWAYS return a valid JSON response from your server. If you are using IE9 or older, be sure to return a response code of 200 as well.