trying to delete a row from a table

Hi,

I am trying to delete a row from a table
delete from tasks where no = xxxxx
and get the error:
ORA-20411: Residual of 1 found. Insufficient data to unallocate.
ORA-04088: error during execution of trigger 'SONICA.TASKS_AF_DEL'. I'm trying to understand the FK referential contraints. Here is a query to show the dependencies from the TASKS table that I'm trying to delete the rows from:

TABLE_NAME: AREA_ZONE
KEY_NAME: AREA_ZONE_PK
REFERENCING TABLE: TASKS
FOREIGN_KEY_NAME: FK_AREA_ZONE_TASKS
FK_STATUS: ENABLED

and the trigger that executes is:

CREATE OR REPLACE TRIGGER "SONICA".tasks_af_del
after delete on tasks
for each row
declare
sLicNo tasks.lic_no%type;
iInvKey tasks.inv_key%type;
begin
if :old.type in (TYPE_PK.rTaskType.put,TYPE_PK.rTaskType.trx,
TYPE_PK.rTaskType.repl) then
if :old.ord_key is not null and :old.ord_type = 'T' then
if :old.unit > 0 then
XORD_PK.Alloc(:old.ord_key,:old.ord_line_no,-:old.unit);
else
XORD_PK.UnAlloc(:old.no);
end if;
elsif :old.dst_location is not null then
if :old.pick_no is not null then
if :old.lic_no != :old.curr_location then
sLicNo := :old.lic_no;
end if;
ORD_ALLOC_PK.UnAlloc(:old.no,:old.pick_no,:old.unit,sLicNo);
else
iInvKey := :old.inv_key;
if iInvKey is not null and :old.ord_key is not null and
:old.ord_type = 'C' then
iInvKey := null;
end if;
end if;
if :old.dst_location != :old.src_location then
LOCATION_PK.Task_Capacity
(:old.dst_location,:old.container,iInvKey,
:old.uom_key,-1,
:old.qty,:old.unit, :old.uom);
end if;
end if;
TASKS_DETL_PK.Del(:old.no);
elsif :old.type = TYPE_PK.rTaskType.pick then
if :old.pick_no is null then
TASKS_DETL_PK.Del(:old.no);
else
if :old.lic_no != :old.curr_location then
sLicNo := :old.lic_no;
end if;
ORD_ALLOC_PK.UnAlloc(:old.no,:old.pick_no,:old.unit,sLicNo);
end if;
if :old.grp_no is not null and RULE_PK.IsAutoRemovePickGrp then
PG_PK.WhenDelTask(:old.grp_no);
end if;
end if;
if INTF_MFCS_FUNC and
TASK_PK.bVoid and
:old.p_no is null and
:old.intf_no < 0 then
TASK_PK.Cancel(:old.no,:old.type,:old.intf_no);
end if;
exception
when others then
ERROR_PK.Raise('TASKS_AF_DEL',sqlcode,'row=' || :old.rowid);
raise;
end;

Can someone help me try to understand what is happening?

Thanks!
Bea Isabelle :)

The ORA-20411 error isbeing raised through a call to RAISE_APPLICATION_ERROR in one of the procedures being called by the trigger -- you'll have to find the code that raises it, maybe by searching through user_source for "20411" or the associated text "Insufficient data to unallocate"