Ok, problem resolved.
sdm.openacs.org and dotlrn.org are still running off of PostgreSQL 7.1.
openacs.org is running under PG 7.2.3 since a few days ago.
The problem was with a wrong setting I changed in the PG 7.1 configuration during the migration of openacs.org to PG 7.2.
I configured dotlrn.org and sdm.openacs.org to be managed under supervise, instead of the ugly inittab hack. I had setup openacs.org to be running under supervise since when the new site was in beta.
-Roberto