There are numerous reasons why SharePoint Portal Server may not be able to index a certain document. The most common problems are
Insufficient privileges to access a page. This may occur on sites where particular URLs are password-protected.
Network or remote server problems that make it impossible to access the site.
“Broken” links included on a Web page.
SharePoint Portal Server Site Path rules that exclude a particular URL.
The file type that is associated with the URL is not supported by SharePoint Portal Server.
URLs that include query parameters. Query parameters are appended to the URL following a question mark (?). Each parameter is separated by an ampersand (&). You will see these constructs typically with ...