The answer to this is very straightforward. The two slaves must have the same [server_id][1]. I wrote about this 2 years ago (https://dba.stackexchange.com/questions/20509/screwed-up-replication-by-sharing-server-ids/20510#20510). In that post, I quoted Baron Schwartz's blog [Pop quiz: how can one slave break another slave][2].

The quick-and-dirty solution ? Change the second slave's [server_id][3]. For example, if the master's server_id is 1000 and first slave's server_id is 1001, go to the second slave and run the following:

    mysql> SET GLOBAL server_id = 1002;

This will fix it right then and there.

Then, go to the second slave and change the server_id in the `my.cnf` 

    [mysqld]
    server_id = 1002

Give it a Try !!!

  [1]: http://dev.mysql.com/doc/refman/5.5/en/replication-options.html#option_mysqld_server-id
  [2]: http://www.xaprb.com/blog/2009/03/14/pop-quiz-how-can-one-slave-break-another-slave/
  [3]: http://dev.mysql.com/doc/refman/5.5/en/replication-options.html#option_mysqld_server-id