Google Droping Cache for some pages

PR,Backward Links unaltered

[webnewton]

This is something unusual which has happened with one of my sites. Google has droped the cache of some of the pages on the site. Here is what is strange
1) All these pages had a PR 3-4 and were is SERPS. They still have the PR, but cache gone when checked from goolge toolbar. and yes toolbar also showing the backword links.

2)These pages are now completly missing from SERPS. I'd done some link building for these pages using keywords in anchortext. Though pages in missing in main SERPS, they are there while i check using allinanchor: keywords(the one's i'd used in anchor). And here Google has the cache for these pages too.

So these pages which were in Google database and for long and were visited regulary by the bot are being droped by google. What could be the reason.

Note: No robot.txt problem here.

[wanna_learn]

webnewton
Nothing new! , its happening with loads of Webmasters, this may help :: [webmasterworld.com...]

Still, you should chk for the Evil Link problem... just in case.

Also, keep tracking if the number of pages in cache are contineously decreasing.

[webnewton]

Why is this happening. Well my site do come in the category of large sites. There is another significant thing here. There are these 20 pages i'm most concened about. You can call them doorways. They all have distinct first two paragraphs which talk about the keyword for which the site has been optimized. Followed by the next 3 paragraphs which are common on all the 20 pages. This means a portion of all these pages is duplicate.
Can this be a reason.
But then one page which is missing is the odd one out and doesn't contain anything duplicate.