Error on XML Parser when referencing external DTD

Hi,

I was trying to replicate some examples I found on the "XML Services" guide. In particular, I'm having troubles to make the parser download an external DTD definition. According to the manual "There are no restrictions on the use of URIs as href attributes or document text, and XML Services resolves external reference URIs that specify http URIs."

But when I execute this query:

insert into text_docs values (xmlvalidate('<!DOCTYPE emp_name PUBLIC "prueba" "http://xx.xx.xx.xx/dtd_emp.dtd"><emp_name>John Doe</emp_name>',option 'dtdvalidate=yes'))

I get this exception:

XMLVALIDATE(): XML parser fatal error <<An exception occurred!

Type:NetAccessorException, Message:Could not create the socket for URL '{0}'.

Error={1}>> at line 1, offset 71.

Using google I found people who got the same error, but I haven't found any solution.

Any help would be appreciated

Thanks

Leandro