Dicebat - 9:20 am on Dec 12, 2011 (gmt 0)
Okay, so the index page is indexed but not ranking the way you want it to rank...
When I read the headline: "Google has dropped our index page", I assumed that your index page got completely de-listed. Which is something I experienced recently (and was hoping to find an answer to).
But for a specific page to not rank the way you expect it to rank... that's a whole different ball game.
I can only recommend that you check what tangor suggested: Ensure the content isn't stale - or better yet, try add a little bit more relevance to the page for what it is optimized for perhaps?
Internal page content are generally more relevant than the home page's headlines and snippets.