chao_ping,

ORA-29740 is an error when a member is evicted from cluster group by another member.
When you look at the trace file towards the bottom you will see the reason as reason 2 as :

*** 2002-12-21 04:02:05.645
kjxgrgetresults: Detect reconfig from 0, seq 6, reason 2
*** 2002-12-21 04:01:57.014
kjxgrrcfgchk: Initiating reconfig, reason 2
*** 2002-12-21 04:01:57.014
kjxgmrcfg: Reconfiguration started, reason 2
kjxgmcs: Setting state to 6 0.
*** 2002-12-21 04:01:57.021

Reason 2 means that an instance death was detected. In other words this instance failed to issue a heartbeat to the CF. When LMON detects that an instance is not issueing a heartbeat,LMON will ping it, if there is a reponse, LNOM will consider the instance alive,
but if the heartbeat is not issued within the threshold of the controlfile_enqueue_timeout usualy set internally to 900 sec (15 min), then the instance will be considered a problem and will be evicted. this is what happened in your case apprantly.

look at the instance alert log. you could disable the eviction by setting a parameter to false, however, this is not recommended since it is a symptom pointing to another problem that needs addressing.

check all the trace files and dumps and determine what caused the instance to fail and be evicted and you'll have you reason.
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ORA-1578
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reason 2