cast needed - but where and why?

Hello list,

I am getting the following error after upgrading from 7.4.6 to 8.3.6
and can't figure out what is wrong. Any help would be greatly appreciated.

from our program:
sqlcode=-400 errmsg='column "event_ref_log_no" is of type integer but expression is of type text' in line 4138.

from pg_log:
2009-04-02 10:45:10 EDT:srm2api:ERROR: column "event_ref_log_no" is of type integer but expression is of type text at character 146
2009-04-02 10:45:10 EDT:srm2api:HINT: You will need to rewrite or cast the expression.
2009-04-02 10:45:10 EDT:srm2api:STATEMENT: insert into t_unit_event_log ( event_log_no , unit_serial_no , event_type
, event_category , event_mesg , event_severity , event_status , event_ref_log_no , event_logged_by , event_date ,
alarm , last_updated_by , last_updated_date ) values ( nextval ( 'seq_event_log_no' ) , $1 , $2 , $3 , $4 , $
5 , $6 , case when $7 > 0 then $8 else null end , current_user , now () , $9 , current_user , now () )

from our program:
exec sql begin declare section;
int h_cnt = 0;
int h_event_ref_log_no = NULL;
...
// insert into uel
exec sql insert into t_unit_event_log
(event_log_no,
unit_serial_no,
event_type,
event_category,
event_mesg,
event_severity,
event_status,
event_ref_log_no,
event_logged_by,
event_date,
alarm,
last_updated_by,
last_updated_date)
values (nextval('seq_event_log_no'),
:h_serial_no,
:h_type,
:h_category,
:h_mesg,
:h_sev,
:h_status,
case when :h_event_ref_log_no > 0
then :h_event_ref_log_no
else null end,
current_user,
now(),
:h_alarm,
current_user,
now());

Thanks,
Steve