If you use & as part of URL e.g. use & in category name, you will get message "HTTP Error 400.0 - Bad Request ASP.NET detected invalid characters in the URL" from IIS7 server. This is because IIS 7 implements UrlScan 2.5 and disallows the ampersand (&) in the request for security reasons. As discussed
here, you will need to do the following two in order to fix this.