Wrong 404 error!!! Please help.

Please help!!

About 2 weeks ago, one zen-cart category page of my website was removed from Google index.
And just now, I happened to try 'fetch as googlebot' in Google webmasters tools to test that page. And it is reported to be a 404 error.

But when I use browser to visit this page, it doesn't redirect me to zen-cart custom 404 page.

Another thing is,
I installed ultimate-seo url rewriter module, and this page's url is rewrited.
The original url is http://www.mydomain.com/index.php?main_page=index&cPath=10 (non 404 error)
Rewrited url is http://www.mydomain.com/***-***-c-10.html (404 error)

It's a same page, but just different urls. While, one is ok, another one returns 404 error.

And what is strange that, only this one page has 404 problem. All other category pages are ok.

Am I hacked?
And what makes this URL 404 error?

Are you sure you installed Ultimate SEO URL's correctly?

To use zen carts custom 404 error make sure you have

ErrorDocument 404 /index.php?main_page=page_not_found

at the top of .htaccess in main site directory.

hi Kenichi

I tried as you suggested, but it didn't help.

Some more information:

1. Zen-cart custom 404 page works well, except this only one page.

2. I just tried to remove .htaccess file, and uploaded a real html file with the same name as the rewrited URL. And then 404 error was gone. When I put .htaccess file back, 404 error is back.

3. My website is 3 years old, didn't have this problem until recently.

I just tried to change the category ID from 10 to 9.
http://www.mydomain.com/***-***-c-9.html
Then the new URL of the same category get a 'http 200 ok'.

So it seems 404 error only happen on category ID 9.

Why?