So, you installed the CM Tooltip Glossary plugin to get nifty pop-up definitions of terms in your posts. Now, after you’ve added your first glossary definition, your site renders empty pages. It took me a while to figure this out, so here you go:
CM Tooltip Glossary requires the DOMDocument class. If it’s not there, your site will be blank. On CentOS, at least, DOMDocument is provided by the php-xml package. Install it and everything will be fine.