Syntax Issue in Trigger Function??

In Postgres 7.3.5 -
When we try to insert a new record into our parties.party table which
is then meant to fire off a trigger to update a column in the table
with some de-normalised information, we get the following error:
ERROR:  FLOATING POINT EXCEPTION!  The last floating point operation
either exceeded the legal ranges or was a divide by zero.

Can someone help spot our syntax erorr, please?

Many thanks!

===============================================
CREATE TABLE parties.party
(
  party_id serial NOT NULL,
  parent_party_id int4,
  party_type char(1) NOT NULL,
  party_name text NOT NULL,
  party_path text,
  modified_by text,
  modified_dtm timestamp,
  created_by text,
  created_dtm timestamp
);
===============================================
CREATE OR REPLACE FUNCTION parties.update_party_ref()
  RETURNS trigger AS
'    DECLARE
        v_party_id         INTEGER;
        v_parent_party_id     INTEGER;
        v_ref             TEXT;

        BEGIN
        /* from the end to the beginning (i.e backwards)
           navigate up the tree of parties adding the party
           ids separated by the backslash character */

        -- we always start with backslash
        v_ref := \'\'/\'\';

        -- grab the first party id to look at
        v_party_id := new.party_id;

        -- set the loop up with an initial read
        SELECT INTO v_parent_party_id parent_party_id FROM parties.party
WHERE party_id = v_party_id AND parent_party_id IS NOT NULL;

        WHILE FOUND LOOP
            -- prefix the ref weve already accumulated with backslash followed
by the parent party id
            v_ref := \'\'/\'\' || v_parent_party_id || v_ref;

            -- the parent party id now becomes the party id one level up
            v_party_id := v_parent_party_id;

            -- look for more parents
            SELECT INTO v_parent_party_id parent_party_id FROM parties.party
WHERE party_id = v_party_id AND parent_party_id IS NOT NULL;
        END LOOP;

        -- now we can perform the update
        update parties.party set party_path = v_ref;

        RETURN NULL;
    END;

'
  LANGUAGE 'plpgsql' VOLATILE;
===============================================
CREATE TRIGGER trg_update_party_ref
  AFTER INSERT OR UPDATE
  ON parties.party
  FOR EACH ROW
  EXECUTE PROCEDURE parties.update_party_ref();
===============================================