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?ma...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?