Looks like you have set the wrong host information in recovery.conf file or there is a mistake in recovery.conf file. Please check your recovery.conf file.
May be postgres should throw a correct message to the logs saying the host information for replication is wrong or something meaningful to understand instead of "database system identifier differs between the primary and standby"
> We are getting the following log while configuring hot standby, > > 2011-04-20 17:34:40 ETC/GMT FATAL: the database system is starting up > 2011-04-20 17:34:41 ETC/GMT FATAL: database system identifier differs > between the primary and standby > 2011-04-20 17:34:41 ETC/GMT DETAIL: The primary's identifier is > 5592072752411433371, the standby's identifier is 5597615802844953578.