After a hard searh, most articles tells us how to modify xmlrpc.php, indeed, it is the solution to wordpress before offical bug solution came out. Unluckly, it does not work to me, who use wordpress 2.6

Thanks to algo pixelado, it works! the article is here

WordPress API for Zoundry Raven, Flickr, ScribeFire

WordPress Version:

WordPress 2.6.3

Problem:

Can not use WordPress API, those Zoundry Raven, Flickr, ScribeFire can not work. When I try https://wwl3.com/xmlrpc.php , it shows that: XML-RPC server accepts POST requests only.

Solution:

login to your dashboard, goto settings/writing/remote publishing

tick the box

“XML-RPC
XML-RPC Enable the WordPress, Movable Type, MetaWeblog and Blogger XML-RPC publishing protocols.”

then test – this worked for me!!