Yes. You are better off using a local (full) path to your folder, for instance:

/var/www/vhosts/example.com/httpdocs/files

If your files folder is outside/ above your webroot (which is recommended), like this:

/var/www/vhosts/example.com/files

Then you'll need to make sure you have access to those files. In normal PHP / Apache setups, there is a directive called open_basedir. What that means is that scripts cannot go outside the directory specified in this directive.

If you have full access to the server, you'll need to change it (either in php.ini, or vhosts.conf).. or you can ask your server admin to take care of it.

Hope this helps.