SEO-friendly URLS not working

I recently changed my permalink settings for my website – http://www.metaphoricalplatypus.com – to SEO-friendly URLs (i.e., http://metaphoricalplatypus.com/sample-post/)

Some pages appear to have converted to the new structure whereas others are still showing up with the default numeric format (either format works to pull up a page). Does anyone know of a solution to this problem?

Thanks!