mod_rewrite results in 404s for bots only

I've recently setup SEF URLs on my website (http://
www.betterthanbroadway.com). They work great for users. Everyone can
use my site with no problems. However, Google and other search
engines are displaying 404's for all of my pages. I get the same
thing when I use the site via an anonymizer service like
Palary.org .

My site relies on cookies and sessions. However, it should be able to
be indexed to some degree without these.

Why am I getting 404s?

Here is my mod_rewrite :

RewriteEngine On
RewriteRule ^event(.*) /index.php$1 [L,QSA]
RewriteRule ^changedate(.*) /index.php$1 [L,QSA]
RewriteRule ^forwarddate(.*) /index.php$1 [L,QSA]
RewriteRule ^descr(.*) /popup_descr.php?parent_event_id=$1 [L,QSA]
ErrorDocument 404 /index.php


I really need some help!

Thanks,
Justin
http://www.BetterThanBroadway.com