PHP fileinfo is undefined function
Have a look at your php.ini file and check that the fileinfo.soor php_fileinfo.dll is activated (depending on your platform and version).
There should be a line similar to
extension=fileinfo.soin your php.ini file
If you using XAMPP, you enable extension=php_fileinfo.dll in php.ini
What version of PHP do you have? PHP 5.3.0 and later have Fileinfo built in, but on Windows you must enable it manually in your php.ini. You can find further information in the documentation.