Some OVAL definitions (like http://www.debian.org/security/oval/oval-definitions-2010.xml\) list the schema version on a separate line:
<generator>
<oval:product_name>
Debian
</oval:product_name>
<oval:schema_version>
5.3
</oval:schema_version>
<oval:timestamp>
2011-10-12T23:46:39.188-04:00
</oval:timestamp>
</generator>
This triggers the schema_version restriction in xml/oval-common-schema.xsd because it does not match the regexp "[0-9]+\.[0-9]+(\.[0-9]+)?".
The attached patch solves this issue by collapsing the whitespace around schema_version.
This patch solves this issue by collapsing the whitespace around schema_version.