We can create temp namespaces and temp objects that contains it. So, for example, temp table will be create at pg_temp_N (N - backendID). But afrer cluster init we have pg_temp_1 and pg_toast_temp_1 namespaces with OIDs 11333 and 11334. Those namespaces are visible from any cluster database, but we cannot create any temp objects (please, correct me).
This is better suited to the pgsql-general or pgsql-admin mailing lists.
Make sure to show your full command(s) and the full, exact text of any errors.