Multiple uploads do not work

Hello, I have created a form here http://www.nafitalia.com/denuncia-sinistro with a few upload fields.

Here is the files config:

field10:jpg-png-gif-doc-docx-pdf-txt
field13:gif-jpg-jpeg-png-tif-tiff-bmp-rle-dib-raw-ico-icon-cdr-psd-pdd-pdf
field14:doc-docx-pdf-odt-ods-odp
field15:doc-docx-pdf-odt-ods-odp
field16:xls-xlsx-xlsm-xltx-xltm-xlsb-xlam-doc-docx-docm-dotx-dotm-pdf-jpg-jpeg-png

Here is the upload path: public_html/images/uploads/

The folder has 644 permission and has a index.html file into it.

However it doesn't work.

What can I do to debug this? Thanks in advance.