Adds some Multisite-specific functions to WordPress' XML-RPC interface.
According to Wikipedia, XML-RPC is a remote procedure call (RPC) protocol which uses XML to encode its calls and HTTP as a transport mechanism. Refer to the WordPress Wiki for further explanation about WP's XML-RPC capabilities.
Maybe the remote publishing function is not enabled. To enable it, chek 'Enable the WordPress, Movable Type, MetaWeblog and Blogger XML-RPC publishing protocols' through 'Writing' menu and click 'Save Changes' (step 3 in Installation).