ORA-31020 when calling DBMS_XMLSCHEMA.registerSchema

  V$VERSION
========
Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - Production
PL/SQL Release 11.1.0.7.0 - Production
CORE 11.1.0.7.0 Production
TNS for Linux: Version 11.1.0.7.0 - Production
NLSRTL Version 11.1.0.7.0 - Production
================================================
Hello, I am getting the error below when trying to register a schema file. The directory object is fine, as I have successfully registered two other schema files from the same location.
Any clues?
Thanks,Leor

BEGIN
DBMS_XMLSCHEMA.registerSchema(
SCHEMAURL => 'http://www.w3.org/2000/09/xmldsig#',
SCHEMADOC => bfilename('U_ICV_DIR','xmldsig-core-schema.xsd'),
CSID => nls_charset_id('AL32UTF8'));
END;
Error at line 11
ORA-31020: The operation is not allowed, Reason: For security reasons, ftp and http access over XDB repository is not allowed on server side