PHP Fatal error: Call to undefined function

Error : PHP Fatal error: Call to undefined function
Solution : The server shows this warning because your script is not working on php4 version so you need to switch to php5 version for the domain who is facing the problem. If on the server both php4 and php5 installed then you can switch to php5 by adding the following code in .htaccess file.
AddHandler application/x-httpd-php5 .php