You are correct that I need session_start(). A simple test shows my session variables are not being saved between requests. However, there is little doubt that the call to session_start() makes the webserver give no response (0 bytes, so no error) to requests. I had a similar issue before that was solved by granting write permissions on a certain folder, but I have verified that is not the issue here. I verified that I am able to write to /tmp and I also changed the session temp folder to one under my root that had write permissions and I still got a 0 byte response. How can I find out what the error is?
I'm also having a much lower priority problem. In my .htaccess file, I have a auto_prepend_file and auto_append_file set. I also have a line that sets .csv and .html to application/x-httpd-php. These files are being properly processed for .html files but not for .php files. This isn't as much of a big deal because I can use require_once or rename my .php files to .html.
I really appreciate the response, Patrick. You've really helped me.