머..데이타 타입 이런건 상관없고...........
리스너쪽에 문제가 있는듯...
리스터 리스타트 해보고...
관련 타입의 데이타에대한 정의 살펴보세요..
크기가 어느정도되는지도 점검해보시구요

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--------------------------- 첫번째 --------------------------------
You are right, ORA-12571 is a common error associated with SQL*Net V2,
SQL*Net thinks the connection is broken while you are inserting lots of
rows into the Oracle database. The default timeout period is 10 secs.
In the Listener.ora you can set a longer timeout period with the line
CONNECT_TIMEOUT_LISTENER = 300 , which means 5 minutes. Myself and others
have encountered this error with the TCP/IP protocol. You raised an
interesting point, that DECNET works ok. without this parameter being
set. But I am a bit surprised that an INSERT of 500 records would cause
this error, normally I would expect many many more.

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I often get the same messages.  I talk to Oracle support and didn't get
much help.  They put blame on faulty network equipment.  What they
suggested is to edit the sqlnet.ora file on the server and the client.
Change the SQLNET.EXPIRE_TIME = 0 and increase
CONNECT_TIMEOUT_LISTENER=300.