Releasing your Invisible Conent
Do you use forms on your website? Are they the only way to get to the content? Even a simple dropdown list of categories will stop the indexing robots in their tracks. Matt Cutts offers some advice on how to unlock your content and allow the spiders to do their business:
Solved: another common site review problem
The actual discussion continues in the Google Webmasters Blog
So, the solution (as always) is to make sure you include text links on your page. Don’t rely on the search engines to interpret your JavaScript dropdowns, forms or even worse, image links.
More advice on Link Building and Navigation in my guide to building an effective website.