I upgraded a Fedora 11 instance to Fedora 12 and found the following error at the top of one of my WordPress blogs:

Parameter 1 to update_comment_type_cache() expected to be a reference,
value given in wp-includes/plugin.php on line 166

The problem wasn’t in a plugin, actually. It was within my theme’s (R755-light) functions.php:

function update_comment_type_cache(&$queried_posts) {

The temporary fix is to remove the & from that line so it looks like this:

function update_comment_type_cache($queried_posts) {

After clearing out the WP Super Cache, the page was loading properly again. It turns out that the function actually calculates how many comments are available for a given post, so that functionality is working properly right now. A few theme authors are already releasing new versions to fix this bug, but my theme’s author has not.

The credit for the fix goes to someone in the WordPress forums.