class-xmlrpc.php error with plugin

I’m currently trying to get the LJautoupdate hack (found here) to work as a plugin, for no real reason other than I’m too lazy to hack my files again right now.

anyway, all I’ve done is put the ljautoupdate function into the plugin file, add global $content, $post_title; to it, and added

add_action(‘publish_post’, ‘ljautoupdate’);

so, I uploaded and activated the plugin (to my testblog which is running 1.2.1, since I hardly use it and haven’t bothered upgrading yet)
Posted a test post, which showed up on the blog but not on LJ. Checking my error log brings up this:

PHP Fatal error: Call to a member function on a non-object in /path/to/wp-includes/class-xmlrpc.php on line 637

any ideas what this means, and whether it’s fixable?