explicit casts

Hi there,

I installed postgresql 8.4 on my box and now i have troubles with the 
following query regarding explicit casts.

select to_char(trunc(to_date(:the_date, 'yyyy-mm-dd'), 'Month'), 
'fmMonth') as month,    to_char(trunc(to_date(:the_date, 'yyyy-mm-dd'), 'Month'), 'YYYY') 
as year,    to_char(trunc(to_date(:the_date, 'yyyy-mm-dd'), 'Month'), 'J') as 
first_julian_date_of_month,    to_char(last_day(to_date(:the_date, 'yyyy-mm-dd')), 'DD') as 
num_days_in_month,    to_char(trunc(to_date(:the_date, 'yyyy-mm-dd'), 'Month'), 'D') as 
first_day_of_month,    to_char(last_day(to_date(:the_date, 'yyyy-mm-dd')), 'DD') as last_day,
trunc(add_months(to_date(:the_date,'yyyy-mm-dd'), 1),'Day') as 
 
next_month,    trunc(add_months(to_date(:the_date, 'yyyy-mm-dd'), -1),'Day') as 
prev_month,    trunc(to_date(:the_date, 'yyyy-mm-dd'), 'year') as beginning_of_year,
to_char(last_day(add_months(to_date(:the_date,'yyyy-mm-dd'), -1)), 
 
'DD') as days_in_last_month,    to_char(add_months(to_date(:the_date, 'yyyy-mm-dd'), 1), 'fmMonth') 
as next_month_name,    to_char(add_months(to_date(:the_date, 'yyyy-mm-dd'), -1), 
'fmMonth') as prev_month_name    from dual

the value assigned to the variable :the_date is '2010-01-05'

The error is

Error: Ns_PgExec: result status: 7 message: ERROR:  function 
to_date(timestamp with time zone, unknown) does not exist
LINE 1: select to_date(date_trunc('month',add_months( $1 ,1)),'YYYY-...               ^
HINT:  No function matches the given name and argument types. You might 
need to add explicit type casts.
QUERY:  select to_date(date_trunc('month',add_months( $1 
,1)),'YYYY-MM-DD') - 1
CONTEXT:  PL/pgSQL function "last_day" line 6 at SQL statement


how would i apply the following solution

date_trunc('month', p_date_in + interval '1 month')::date - 1

to fix the query above?

cheers,
iuri