To Enable FND debug:

1.Navigate Responsibility: System Administrator > Profile => System
a. Find the FND profile options for User who is submitting the process to debug.
User: User submitting the process
Profile: FND:%Debug%
b. Set the following Profile values at the user level
FND: Debug Log Enabled :Yes
FND: Debug Log Filename : NULL
FND: Debug Log Level : STATEMENT
FND: Debug Log Module : %
c. Save.

2.Get the current log sequence in the FND table.
select max(log_sequence) from fnd_log_messages ; -- start

3.Reproduce the issue be sure you get the "FRM-40735: PRE-FORM TRIGGER RAISED Unhandled Exception ORA-04063" error message.

4.Get the sequence in the FND log
select max(log_sequence) from fnd_log_messages ; -- end

5.Disable FND Debug by resetting the above profiles.

6.Spool the output of the following query to an excel file which gives FND debug log:
Run this script and replace start and end with the sequences you obtained from steps 2 and 4.

set linesize 4000
set verify off
set feedback off
set pagesize 999
set markup html on entmap on spool on preformat off

spool val_excess_report.xls

select module, message_text
from fnd_log_messages
where log_sequence between <start> and <end>;

spool off;