'record old is unassigned yet' when using trigger in 7.1.1

I have a function used in a trigger that looks like this:
      begin      IF OLD.status <> NEW.status     THEN    NEW.statchangedate = CURRENT_DATE;     END IF;return NEW;end;

The problem is when a new row is inserted I get this error message:
ERROR:  record old is unassigned yet
... and the insert fails.

It doesn't matter if the trigger is before or after.

-- 
Joseph Shraibman
jks@selectacast.net
Increase signal to noise ratio.  http://www.targabot.com