fmgr_info: function 7390843: cache lookup failed

I am getting this error:

fmgr_info: function 7390843: cache lookup failed

when trying to insert some data into a table using the tsearch2 contrib
module (this is postgresql 7.3).   I have the following trigger defined:

     BEGIN
         NEW.search_vector :=
setweight(to_tsvector(coalesce(NEW.display_text, '')), 'A') ||
to_tsvector(coalesce(NEW.content_desc, ''));
         RETURN NEW;
     END;

Which I suspect is causing the problem.  Where can I look up that
function number to verify this?  Any suggestions?

culley