Problem running "ALTER TABLE...", ALTER TABLE waiting

Hello,

I'm running Postgres 9.0.2 on RHEL 5.6 x86_64 and trying to run the
following statement:

alter table samples add column in_esp1234 text;

When I do this the command just hangs. ps output indicates that it's
waiting:

postgres: postgres exomeSNP [local] ALTER TABLE waiting

When I look to see what might have that table locked I don't see anything:

select * from pg_locks where relation=(select oid from pg_class where
relname='samples');

I have a nearly identical server where this command works. It seems like
something has this table locked, but I haven't been able to find it. Any
ideas?

Thanks for any help,

--
Brian McNally