"Cannot determine registration class!" - this error occurs if you install the extension. The bundled extension has the error mark in the extension manager. JavaScript works fine, nevertheless.
Forgot to mention: this is LibO3.4 beta4 + Ubuntu 10.04
Fixed by this commit in 3.4 branch http://cgit.freedesktop.org/libreoffice/libs-core/commit/?h=libreoffice-3-4&id=39c7949d6cfe4ef0421e53bdca70b4b06568b9bc