postgres jdbc transaction problem surfaces at times

i read in the posts here that postgres 8.0 jdbc had unmasked it;s
dislike of changing transaction level mid transaction so i changed my
code to the following

is this set up correct?

try {
livedb.setAutoCommit(false);
copydb.setAutoCommit(false);

livedb.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);

copydb.setTransactionIsolation
(Connection.TRANSACTION_SERIALIZABLE);

// series of writes to both db's

livedb.commit();
livedb.setAutoCommit(true);
copydb.commit();
copydb.setAutoCommit(true);

} catch (SQLException sqle){
// run a rollback-Release and log it routine;

// crash and burn;
}

this seems to work fine single user, but with several users on i get
occasional dumps with
transaction change in transaction.

the only code to change relates to the LUW start since the last rollout
of this servlet and there was never this problem before.
the connections are stored as a session attribute, so persist across
requests.