Chris Finke posted on Netscape blog answer to the tech community about the dumped RSS DTD which caused problems in few feeds around the web and make them not parsing correctly. The DTD for RSS 0.91 have been removed accidently while moving to new servers, while many applications and services are based on cached copies of the dtd to parse RSS, it happen that some of them still request the dtd from netscape servers to ensure a correct parsing.

In the future you have to keep a cached copy of the DTD or grab it from web archives, since DTDs for RSS 0.9 and 0.91 will be available via my.netscape.com until July 1, 2007 only.

Over the weekend, the tech community noticed that a file crucial to the operation of certain RSS readers was MIA. This file, the DTD for RSS 0.91, had been hosted at my.netscape.com, and its purpose was essentially to explain the structure of RSS 0.91 documents and to provide definitions for a set of character entities that could be used in such documents.

Theoretically, RSS readers load this file when parsing an RSS 0.91 feed. However, In practice, most readers (including those built into Firefox and Internet Explorer) either just ignore the file or load their own cached copy.