Architecture / Installation

Hello — I've noticed that sometimes, when navigating to wiki pages, I get the following error, and also that the problem is easily cleared up by refreshing my browser: can someone tell me what this error means and what might be causing it? Is there any way to prevent it from occurring?

Fatal error: session_start(): Failed to initialize storage module: user (path: /tmp) in /home/ajdrake/public_html/wiki/tiki-setup_base.php on line 201

Thanks