Reasons Pages may not be reachable
  1. Links in submission-required forms: Crawlers will not submit forms, so any content or links that would be accessible after the submit of a form will be invisible to the engines.
  2. Links in un-parseable javascript.
  3. Links pointing to pages blocked by the meta robots
  4. Links in frames or I-frames
  5. Links only accessible through site search
  6. Links in flash, java or other plug-ins
  7. Links on pages with lots of links