It's a php setting in php.ini.
You have to edit your php.ini file and enable it in there. You need root access for this. If you don't have that, ask your hosting provider.
The main reason for turning dynamic loading off is security. With dynamic loading, it's possible to ignore all open_basedir restrictions. The default is to allow dynamic loading, except when using safe mode. In safe mode, it's always impossible to use dl().
You're welcome.
It's set to off for security reasons. Next to that this feature is deprecated and will be disappearing in the future.
As from the php.net manual:
Remember to restart the httpd service after making and saving changes to the php.ini.