The following paragraph is from SEO Google Guide
Google is good at crawling all types of URL structures, even if they're quite complex, but spending the time to make your URLs as simple as possible for both users and search engines can help. Some webmasters try to achieve this by rewriting their dynamic URLs to static ones; while Google is fine with this, we'd like to note that this is an advanced procedure and if done incorrectly, could cause crawling issues with your site.
What makes URL re-writing implementation incorrect for GoogleBot? I am using Asp.net 3.5 framework.