You receive an error "ORA-03114: not connected to ORACLE" when you are trying to connect to the Oracle database with Biztalk Oracle Adapter. This error can occur even if you was connected to the database just few seconds ago.
Problem relates to the connection pool.
If the connection pooler detect that the connection with the server has been broken it will remove the broken connection from the connection pool. This doesn't happen all the time and you actually get a bad connection from the pool.
Workaround is to change Send port settings: Change useOracleConnectionPool to false at Bindings tab