I checked all fields and they seems good.
But 1 more detail!!!

We have message:
ora-06512: at webuser, cust_tri_iu line 28 (!!! line = 28)

in triggers source code :
------------------------------------------------
1. CREATE OR REPLACE TRIGGER cust_trig_iu
2. AFTER insert or update on CUST
3. For each row
4. BEGIN
5. IF INSERTING then
6. INSERT into CUST_INTERFACE (
7. d,f_name,mi,l_name,inst_id,pay_freq,lookup2,lookup3,action_code,insert_type,time_stamp)
9. VALUES (:new.c_id,:new.f_name,:new.mi,:new.l_name,:new.inst_id,:new.pay_freq,:new.lookup2,:new.lookup3,:new .action_code,
'I',to_char(sysdate,'DD-MON-YY HH24:MM:SS'));
9. ELSE
10. INSERT into CUST_INTERFACE (
c_id,f_name,mi,l_name,inst_id,pay_freq,lookup2,lookup3,action_code,insert_type,time_stamp)
11. VALUES (
:new.c_id,:new.inst_id,:new.f_name,:new.mi,:new.l_name,:new.pay_freq,:new.lookup2,:new.lookup3,:new. action_code,
'U',to_char(sysdate,'DD-MON-YY HH24:MM:SS'));
12. END IF;
13. END;

we have less lines.
My question - are u check source code in database or not?