ORA-3114 error

I am using Oracle 8i(version 8.1.7) on windows NT.We have a ERP application made in oracle itself. From past 3-4 days users are facing problem of "ORA-3114 not connected to oracle" suddenly as soon as they fill up account no(field in application). Application developers are claiming that application is all right and some batch file needs to be updated.Kindly note that RTRIM(UPPER) function is used for that field in application.Can anybody guide me what needs to be done.
Thanks & Regards,
Saurabh Verma

yes, you trace their sessions