On the King Design web site I use a set of custom rewrite rules to hand off URLs to the WordPress back end. I never had any trouble with this through versions 1.5.x, but when I upgraded to 2.0.x, I ran into some trouble.
As it turns out, I ran into more trouble than I had realized.
It appears that ever since the upgrade, all pages on kingdesign.net have been returning 404 error messages along with the page content.
Doh!
I’ve “fixed” this by changing the status_header function to suppress the 404 header, which isn’t much of a fix.
Point is, it looks like my previous 
solutions 
FYI – can’t even get to the KingDesign homepage right now.
There are gremlins, gremlins I say! wreaking havoc all over the internets!
I had quite a few rewriterule problems when I upgraded to v2. If you have a poke around the WordPress.org forums you can probably find the solution there.
I just discovered the same thing today that a plugin I made was doing this as well, a result of the tricky changes in WP2.
I added a filter for “query_vars” and set $error=” and I think the 404 is gone now.
I wish WP would revert to its much simpler days. Even working with the rewrite rules now seems like a daunting task.
Hey, same story goes here.
Does it mean that upgradation is not better though!!
What can i do to solve it?
I am not at all technical perosn either.
Please, tell me how can i solve this 404 error?
It is really irritating & i am wired.