Oracle Database Discussions

Hello gurus, after upgrade our clients for oracle 11 we start getting aleatory "ora-00942: table or view does not exist." on the application, this happens ever day since upgraded, just finished upgrade, and some clients start getting this error once a day at least 2 or 3 clients get this errors.
the oracle server is 11.2.0.1 running on hpux 11.31. clients had oracle 9 run time installed before and was uninstalled and installed the new client oracle11.

looking at alert log we don´t have any problem on database side. the table that error tells is avaiable , i disabled and enabled constraints and it back to work immediatly.

so far i have no idea if there is something that i can do on database side, or this is something related to oracle client, application or what ever could be.

application log is always the same always sql error: ORA-00942. but tables always there, and avaiable via sqlplus or pl/sql. so far no clue i keep doing disable/enable constraints and all back to work for couple of time.

please send me your ideas or experiences.

thanks a lot for your help.