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All In One SEO Pack is another good free plugin that allows you to directly edit the meta description tag on each page

I had a similar problem recently and got a great response here;

http://www.seomoz.org/q/identifying-why-my-site-has-a-penalty

I think my site is recorvering, but it's early days still. Anyway, there's some great advice in the link above

Oh yeah, right! That's funny, I wonder how that happened. I had a quick peak in Yoast and the various post types and pages were set to no-index. You're a star, thanks a million.

Let's see what happens...