Could you post the query that failed when you mounted the subsite? From the query that failed on unmount it appears that the after_mount callback failed to make the members group for the new subsite.
Also ... which version of OpenACS did you upgrade from? 4.6.2?
I tested the upgrade scripts when I ran them but did *not* test the added complexity of first upgrading from PG 7.2 to PG 7.3. The query and error that failed on mount may shed some light on what's wrong ...
