Query error corrected after vacuum

Hi,

I'm getting the following error:

select name from files where dir_id =
(select id from dirs where domain_id =
(select id from domains where domain = 'foo'))

ERROR: ExecReScanSetParamPlan: extParam list of plan is NULL

My test program drops the relevant tables, then recreates them before performing the above query. I don't get this error if I run vacuum after creating the "dirs" table. This problem sounds similar to an old post I found:

http://looking-glass.usask.ca:82/mhonarc/pgsql-general/1999-02/msg00318.html

Please respond via personal email. Thank you for you help,

Matt