Yesterday I attempted to connect to my MSN account with pidgin and received the error “Unable to retrieve MSN Address Book.” After a bit of research I found that Microsoft has prevaricated parts of the MSN protocol in turn for the WLM protocol.
In order to fix this issue, you must switch your protocol to WLM from MSN. If you don’t have the WLM option in the ‘add account’ dialog box install the X11 plugin for msn-pecan. (Under Gentoo this is: x11-plugins/pidgin-msn-pecan)
After this install, a restart of pidgin, and creating a WLM pidgin account I was able to resume chatting happily.