I checked the wedge_pretty_topic_urls table and everything looked good. I truncated the table, enabled pretty URLs on topics, and then recreated the topic subjects. The table got populated with the topic IDs and all the pretty URLs, but the problem came back. I could on browse topics created for the last 2 days. Nao, I am not sure if this is relevant, but all posts with id_topic 2000 or higher stop working when pretty URLs on topics is enabled. Any topic with id_topic 1999 or less still works and can be browsed. I have disabled pretty URLs for now.