Why Visual Studio doesn't like this XML schema? (Prefix '' cannot be mapped to namespace name reserved for "xml" or "xmlns")

FictionBook (also known as FB2) is an XML-based format of electronic books. Its schema can be found here:

http://gribuser.ru/xml/fictionbook/2.0/xsd/

However, when I downloaded this schema and tried to open it in Visual Studio 2012 I got a bunch of errors, the first of which was: Prefix '' cannot be mapped to namespace name reserved for "xml" or "xmlns". Line 5, position 118. E:\dev\fb2\FictionBook2.xsd.

Is the schema really invalid? If so, how is it possible that a lot of software use it to validate FB2 files? Is there an easy way to modify the schema to make VS happy?