you must upgrade to pidgin 2.5.8 which is available in debian unstable (sid).
add to /etc/apt/sources.list

deb http://ftp.debian.org/debian/ sid main contrib non-free

#apt-get update
#apt-get install -t sid pidgin

change the pager server to

scsa.msg.yahoo.com

Error 1013 - just remove the @yahoo.com on your pidgin login username