I expect this is an issue with using an unpatched release of Oracle
(this should be patched up to 10.2.0.3), however this is a known issue
with iSQLPlus (and a reason it's no longer included with future
database releases). You might try starting it with this command:
nohup $ORACLE_HOME/jdk/bin/java -Djava.awt.headless=true -Xrs -
Doracle.oc4j.localhome=$ORACLE_HOME/sqlplus -Djava.security.properties=
$ORACLE_HOME/oc4j/j2ee/home/config/jazn.security.props -jar
$ORACLE_HOME/oc4j/j2ee/home/oc4j.jar -config $ORACLE_HOME/oc4j/j2ee/
isqlplus/config/server.xml &
and see where that takes you.
And I have found no advice from Oracle regarding any configuration
files and the number of allowed threads.
David Fitzjarrell