If you are PHP Developer than you might aware with php versions and theirs functions. If your server have php4 and php5 versions than php4 is the default version. In this case, you are not able to access php5 functions which throws an error while you compare it with local server and live server.
There is an easy way to change php version runtime by using .htaccess. You can switch from php4 to php5 version by using htaccess rule. Just copy and paste below line if you want to change php version from php4 to php5.
AddHandler application/x-httpd-php5 .php .php5 .php4 .php3
Once you put above line, and check phpinfo using phpinfo() function. You can see that php version is changed. It should be php5 version now.
If you face any problem with this, let me know. I would love to help you with any issue you faced.