error executing plpgsql function

Hello,

I'm using postgresql 6.4. I can define a plpgsql function, but when I
execute it I get the following error:

dbchse=> select rango (0);
ERROR: fmgr_info: function 5410395: cache lookup failed

The language is properly defined, and the function works fine with
another machine running postgresql 7.0

What can be the problem?

PS: I don't know if there is any relation, but If try to do a vacuum I
get the error:

dbchse=> vacuum;
ERROR: Can't create lock file. Is another vacuum cleaner running?
If not, you may remove the pg_vlock file in the
/usr/local/pgsql/base/dbchse

Thanks

--
Salva