404 error on a single post of a category

I have run into a strange problem. I have multiple posts in a category, but a single post returns 404 error on clicking it. I am using custom permalinks (index.php/%postname%/). The website is running in windows server.

the link that shows 404 error is http://a1enterprises.net/sushi/index.php/sushi-in-las-vegas-sushi-restaurant-anniversary/

where as other posts under the category blog (the link —> http://a1enterprises.net/sushi/index.php/category/blog/)gives the full article.

Please help