warning on serializer - unable to access extension

[radarjd]

I got the following:
Warning: require_once(XML/Serializer.php): failed to open stream: No such file or directory in /usr/local/www/ext/thebrig/extensions_thebrig.php on line 10 Fatal error: require_once(): Failed opening required 'XML/Serializer.php' (include_path='.:/etc/inc:/usr/local/www') in /usr/local/www/ext/thebrig/extensions_thebrig.php on line 10
on http://nas4free/extensions_thebrig.php

This is a new install into embedded NAS4Free 10.2.0.2 (2545) (NAS4Free-x64-embedded-10.2.0.2.2545.img.xz)

Any suggestions? thanks!