The snippet text you are referring to can come from the following places:
Can come from many different places depending on the situation
- If the crawler can access the URL
- Meta Description Tag
<head>...<meta name="Description" content="Your Description" />...</head>
- Pull the description from within the page
- Tries to pull the most relevant part of the page.
- If the crawler can't access the URL
(robots.txt, site was down, etc...)
Webmaster Tools Account and Sitemap Setup
Setting up a Webmaster tools account and Sitemap would do alot to fix this.
Change the Crawl Rate
Also try to increase the frequency with which Google crawls your page using
Webmaster Tools->Settings->Crawl Rate (but not so much that it overwhelms the bandwidth of your site)
You can also find out when the last time Google has crawled your site was by visiting the cached version of the page in the search results.
(Note however that you can't change the crawl rate of a subdirectory of your site, you can only change it from the root url of the site).
Reduce redundant crawling of pages
Set at Canonical URL/Domain
Setting a Canonical Domain for your site can reduce reduce redundant visits from the Google crawler.
Setting a preferred URL (a Canonical URL) for pages can reduce redundant visits to the same information that can be reached by various URLs.
Also, if your site has alot of non-standard parameters for changing what sort of content is displayed a page, it's possible that Google is running out of resources for crawling your site, so you should configure your URL parameters.