SOLUTION

Cause    1 - Users close the browser before exiting the Form gracefully.

Solution  1 - Educate users not to do this. Also, to prevent users from doing this, implement the steps in note 605327.1 How To Trap Attempts At Closing The Parent Browser Running A Forms Application.

Cause    2 - heartBeat is greater than FORMS_TIMEOUT.

Solution  2 - Although one can terminate idle Forms sessions in this manner, this results in an aborted termination and will cause the FRM-91230 error.  This is not a recommended method of terminating idle Forms sessions.  It is recommended that FORMS_TIMEOUT be set greater than heartBeat.  For example, FORMS_TIMEOUT=15 and heartBeat=5.  If you wish to terminate idle sessions then implement the timeout bean.   For 10gR2, the timeout bean can be downloaded from Timeout Bean.  Another option it so set up a Database Profile as described in ->

How To Use PROFILES To Limit User Resources Note 1016552.102.

Cause    3 - Please review  Note 1245895.1 for a situation that can cause this error.  Normally, the client user will see a hanging condition.

Solution  3 - See solution listed in Note 1245895.1 

Cause    4 - Please review Note 1171063.1 for a situation that can cause this error.

Solution  4 - See solutions listed in Note 1171063.1.

Cause    5 - Inappropriate Timers in Forms.  Timers should be used judiciously in Forms or replaced with JavaBeans. 

Solution  5 - The number of them and their duration and frequency should be as small as possible. The best solution is to replace them with JavaBeans.  See Oracle Fusion Middleware Forms Services Deployment Guide 11g Release 1 (11.1.1), section 14.2.4 Other Techniques to Improve Performance -> Examine timers and replace with JavaBeans.

Cause 6 - Network issues.

Solution 6 -Sometimes setting networkRetries=15 in the formsweb.cfg can resolve this.