Hello
I think you need contact to your provider hostting and tell the problem. Because your hosting current is not support this function strpos in joomla and you can see it here:
stackoverflow.com/questions/10255831/fatal-utf8-strpos-error
And in my component we change JString::strpos of joomla to strpos of php and now it work fine. you can check it
You can see code we changed in line 153, 199
$metadesc = substr($metadesc, 0, $limit_description);
in file: administrator/components/com_joautofacebook/helpers/joautofacebook.php
Best regards
Bach Pham