[Plugin: Default Post Content] error with WP 2.8.4

Default post content not actually saved when ‘Save’ button clicked, and new error pops up in Add New Post page:

call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, ‘my_default_post’ was given in /…/wp-includes/plugin.php on line 166

http://ww.wp.xz.cn/extend/plugins/default-post-content/