XLSX file upload not working.

Hi,
I have been using simplexlsx class for importing excel datas. But for past few days i have problems in importing documents with .xlsx extension.while .xls files work perfectly. When i try to upload .xlsx file, it shows a error message like "Warning: Invalid argument supplied for foreach()".
Small part of my coding is
require_once('../includes/excel/simplexlsx.class.php');
$xlsx = new SimpleXLSX('../includes/excel/uploads/'.$file_name);
It tells that the variable $xlsx->rows() is empty,but i am sure that $file_name has a valid file which contains data.I have updated my class file by replacing a new one too.Nothing happens.
Please help me regarding this.
Thanks :)

Class support .xlsX files only
old .xls is not reading

* try rename your file to .zip and open

Thanks Sergey. I tried renaming the file but the problem still exists. Is there any update i should do for the class file?

Thanks :)

try open your workbook.xlsx in MS EXcel

Thanks Sergey.Yes. i can read the contents in Ms Excel. and i can open the document in open office too.