Is this after you've uploaded files or are you trying to browse the directory?
If it's after uploading files make sure you've uploaded them using the correct account (not root) so that they are owned by the correct user.
If you're trying to browse the directory, if I remember, cPanel defaults to directory browsing off. If you want to be able to do so then there should be a switch in WHM to turn it back on.
Additionally you can take a look at the Apache error log which should be at /usr/local/apache/logs/error_log.
Hope that helps!