How to remove VACUUM lock?

Hi guyz,

Because of some strange reason my VACUUM command resulted in a complete
halt of the database PostgreSQL 6.3 on Linux 2.0.18 (already a simple
select * resulted in a halt). I had to manually close the postmaster and
all the locked backends before I could access my database again.

Now the select * query works again, but issuing "vacuum" gives:

Welcome to the POSTGRESQL interactive sql monitor:
  Please read the file COPYRIGHT for copyright terms of POSTGRESQL

   type \? for help on slash commands
   type \q to quit
   type \g or terminate with semicolon to execute query
   You are currently connected to the database: komal

komal=> vacuum;
ERROR:  can't create lock file -- another vacuum cleaner running?
komal=> vacuum;
NOTICE:  CreatePortal: portal <vacuum> already exists
ERROR:  can't create lock file -- another vacuum cleaner running?
komal=> 

What can I do to remove this portal ?

Philip