Search ranking issues

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Hello
Our wordpress blog was doing great until novemeber 2012 . here is quick stats linkstats

so what happend without knowing that chaning parmalink will cause problem within search engines we have changed to archive/post to %post name%

Know ranking just vanished from 9,000 queries indexed to just 110 queries are showing up and keyword language has changed . also pages are showing up like this click here
witch most of the time gives 404 error to gogole . Webmaster tool shows 400 crawl errors because nothing is appearing there