I cant import products with import/export tool

I receive this erorr when i try to import products from file....

Fatal error: Class 'PHPExcel_Calculation' not found in /home/pcbox/public_html/system/PHPExcel/Classes/PHPExcel.php on line 360

Thank you and pls help

On the extension page, the author of that mod has asked in very bold letters that you contact him directly for support as he doesn't frequent the forums.