[Andy Peatling]

This is a bug in the libxml2 library on your installation.

http://josephscott.org/archives/2008/12/problems-with-libxml2-for-wordpress-xml-rpc-users/

You can upgrade this on your server – but – make sure you have enabled the “BuddyPress enable” plugin on the bbPress side, as this is a temporary fix for the problem.