XML Schema Validation

I'm using the xml schema and the xml file (Nascita.xml) here attached.

I've tried to validate the xml file using the W3C Schema Validator 
(http://www.w3.org/2001/03/webdata/xsv) and libxml 2.6.26 
(http://www.xmlsoft.org)

The results are different:
- the W3C Schema Validator validates my file
- libxml2 validator returns "The schema document 'BaseTypes.xsd' cannot 
be imported, since it was already included or redefined"

Anyone can help me to understand why this happens? And how to solve or 
avoid my problem...
Thank you in advance.

-- 
Andrea Nucci
Ancitel S.p.A.

Tel. 06.7887336
nucci@ancitel.it

http://www.ancitel.it