Normally, when a URL is typed or pasted into a facebook status update field, facebook creates a preview of the page below the text. After doing this, the fb user can delete the URL and the preview will persist. Sometimes, fb provides a control to cycle through other images scraped from the URL, and the user has options to exclude the preview image, or the entire URL preview.
But sometimes, pasting a URL has no apparent effect - a brief progress animation appears in the upper-right corner of the status update window, but no preview appears. This is apparently due to either malformed code in the web page, or a deliberate attempt on the part of the creators of the page to prevent facebook previewing.
One trick I've discovered that might help you is that if you paste the problem URL into a "URL shortener" utility like Google's goo.gl or Bitly, then paste the shortened URL into the facebook status update field, the preview functionality returns in most cases.
Be safe out there.