Cannot DROP while process running

I am on Postgres 9.1 and running into a problem when trying to drop a table
in my public schema.

When I issue the drop command for a table, the server doesn't respond - not
even with increased disk activity or CPU usage. I am wondering if a lock is
blocking it? When I select from pg_stat_activity the table I am intending
on dropping is not listed as having anything actively using it.

The only table with a lock or any activity is 'public.raw_tomtom'.

mapping=# select datname, procpid, current_query from pg_stat_activity;
datname | procpid | current_query
----------+---------+----------------------------------------------------------------------------------
postgres | 3944 | <IDLE>
mapping | 3945 | <IDLE>
mapping | 16193 | SELECT * FROM public.assign_vertex_id('raw_tomtom',
0.00001, 'the_geom', 'gid');
mapping | 25456 | <IDLE>
mapping | 20897 | autovacuum: VACUUM ANALYZE public.raw_tomtom
mapping | 20405 | LOCK TABLE public.vertices_tmp IN ACCESS SHARE MODE
mapping | 19461 | LOCK TABLE public.vertices_tmp IN ACCESS SHARE MODE
mapping | 17570 | <IDLE>
mapping | 20466 | LOCK TABLE public.vertices_tmp IN ACCESS SHARE MODE
postgres | 20874 | <IDLE>
mapping | 20976 | select datname, procpid, current_query from
pg_stat_activity;
mapping | 20609 | <IDLE>
mapping | 20876 | <IDLE>

*procpid 16193 "SELECT * FROM ..." is a long running process that would not
be touching the table I am trying to drop.

Thanks for any help!

--
Steve Horn