Sometimes the Y!M pager server is down for maintenance. Therefore Pidgin clients encounter connection problem.
You may fix it simply by changing the pager server settings:
(Account -> Manage -> -> [Y!M account] -> Modify -> Advance)
change to: cn.scs.msg.yahoo.com (22.214.171.124)
or: cs101.msg.cnb.yahoo.com (126.96.36.199)
P.S: Kopete or Empathy clients issue can be fixed in a similar way, too.
4 months ago