Note: The problems described in this document are fixed in Pidgin 2.5.7.  You should upgrade immediately to continue using Yahoo! IM.

As of June 17, 2009, Pidgin users are having trouble connecting to Yahoo! IM accounts.  Here is a summary of the problem:

Yahoo! appears to be upgrading their servers to a new version of their software.  This new version requires a new authentication method.  The latest version of Pidgin, 2.5.6, does not support this new authentication method.  The next version, 2.6.0, will, but it has not yet been released. Version 2.5.7 does.  To continue using Yahoo! IM, upgrade to this version.  See the Pidgin web-site for details.

Some reason that the problem have be published which Pidgin and Yahoo(1) simple copy from WWW. in some day ago.

source:http://www.celticwolf.com/useful-information/faqs/26-pidgin-yahoo