Major Problem - Indexed Pages Number Dropping in Google

Hi - I installed the sitemap plugin on Saturday and everything seemed ok, but today I noticed that in 2 days my site has gone for 26,100 index pages in Google to 16,100. It appears that all the showthread pages have been dropped!

Here are the stats for the last sitemap generation:

Date2008-04-03 01:00Processing time307.49 sTotal URLs587,733 (+229)Forumdisplay URLs11,067 (+3)Showthread URLs301,937 (+118)ShowPost URLs0 (-)Archive URLs274,728 (+1)Member Profile URLs0 (-)

What is going on? The last thing I expected this software to do would be to negatively impact search results. I have vBSEO install too btw.

Please help.

Also, I've just seen in the Google webmaster tools that it says I have 8625 pages indexed from my site map. I'm pretty sure this was around 25,000 or more yesterday.

Google is indexing on my site at around 7000 pages a day, and it is indexing showthread pages, so I haven't accidentally blocked Google from those.
Has Google desided to start over of something?

Please help. :(

This is my robots.txt content.

User-Agent: *
Disallow: /forums/attachment.php
Disallow: /forums/avatar.php
Disallow: /forums/editpost.php
Disallow: /forums/member.php
Disallow: /forums/member2.php
Disallow: /forums/misc.php
Disallow: /forums/moderator.php
Disallow: /forums/newreply.php
Disallow: /forums/newthread.php
Disallow: /forums/online.php
Disallow: /forums/poll.php
Disallow: /forums/postings.php
Disallow: /forums/printthread.php
Disallow: /forums/private.php
Disallow: /forums/private2.php
Disallow: /forums/report.php
Disallow: /forums/search.php
Disallow: /forums/sendtofriend.php
Disallow: /forums/threadrate.php
Disallow: /forums/usercp.php
Disallow: /forums/images/
Disallow: /forums/sendmessage.php
Disallow: /forums/register.php
Disallow: /forums/subscription.php
Disallow: /gallery/data/
Disallow: /gallery/images/

Strange - it is up to 17,300 pages now..... Is it recompling info or something?

Starting to think this is a Google glitch. It is up to 24,900 now.... had me worried!

a drop is 100% normal.

Keep in mind, you have TONS of duplicate content out there right now. With every post per thread, you add another way of getting there.

(ie,
showthread.php?t=123
showthread.php?p=456
showthread.php?p=457
)

vbseo cleans that up to one/url/ so your 3 there become 1.

the first month, expect a roller coaster. You will peak, you will fall, and at the end of the day, you'll end up with true figures in the SE's