Logical standby database not applying

Hello Experts,

   Our logical standby database halted the apply, I couldnt see any event in dbs_logstdby_events and the output of v$logstdby_state is

   SQL> select * from v$logstdby_state;

PRIMARY_DBID SESSION_ID REALTIME_APPLY                                                   STATE
------------ ---------- ---------------------------------------------------------------- ---------------------------------------------
                                 1             N                                                                APPLYING

   I could see some entries in the alert log as

  LSP0: warning -- apply server 3, sid 280 waiting for event (since 10944 seconds):
LSP0: warning -- apply server 5, sid 356 waiting for event (since 10944 seconds):
Thu Jun 21 09:09:52 2012
LSP0: warning -- apply server 2, sid 240 waiting for event (since 560 seconds):
Thu Jun 21 09:38:54 2012
LSP0: warning -- apply server 1, sid 201 waiting for event (since 1742 seconds):