I don't know how the site could still be working.... but your first error there refers to the config file for aolserver. View your Aolserver config file (possibly named nsd.tcl) and check your
ns_section "ns/db/drivers"
ns_param postgres
And make sure the path to your postgres driver is correct. Should be something like
${bindir}/postgres.so
Which would mean your file is something like
/usr/local/aolserver/bin/postgres.so
HTH