I have a prestashop website http://www.mumsnbabysupermart.com.au/. The website was fully functional BUT suddenly website stop working and shows a fatal error. The error is-
Fatal error : call to undefined function mb_convert_encoding() in home/xxx/xxx/public_html/cache/smarty/comile/94/23/30/942330f3aff64545a59bff57a8a2078fb44cd308.file.heeader.tpl.php on line 78.
I did googling but found nothing. In this website i integrated Australia Post, eWay and Paypal.
Do you have mb_string enabled on your server?
If not, you'll need to contact your service provider and ask they to enable it.
Think about debug mode, too: http://doc.prestashop.com/display/PS16/Performance+Parameters You may disable non Prestashop modules and overrides.
If you still receive this error, use "Force compilation" in Smarty and disable cache.
Did you update PrestaShop recently?