Highest placed pages dropped from search engine...?

I checked the pages indexed in MSN for my website today and noticed that my top 3 performing pages have all been DROPPED from the MSN indexes (useing the site:www.xxxxxx.com). Previously I was getting several hundred visits a day from these pages as they were in the top 5 for comptetive keywords. Now they are 100% gone but all my other pages are still there. Of all the things... my poor performance pages weren't touched, but my money pages were. Does anyone know how this could happen?

Also... is it possible for someone to make it appear that these web pages were spamming or emplying some black-hat techniques (which none were) and thus got those pages banned? Any help much appreciated! I'm determined to find out where and why those pages vanished.

My homepage and all of my popular pages are NOWHERE to be found on MSN. Only my least trafficked pages still exist.

I have a pretty well established site, we've got a PR7, we've been around for 6+ years, etc.

Now I've got some 'splaining to do.

No black hat tactics, pure backlinks and SEO, not to mention my other clients haven't budged.

I've heard plenty of reports of dynamic drops and gains since early last week, so something is certainly up.

Can someone who's experienced a gain in that window of time explain what kind of SEO tactics they focus on/avoid all together? We've got to get to the bottom of this.


HELP PLEASE!!